A cellphone has been found near the site of one of Friday's Paris shootings with a map of the music venue that was attacked and a text message on it saying words to the effect of "let's go", a source with knowledge of the investigations said.
Confirming reports on French web site Mediapart and U.S. television channel CNN, the source said the phone was found in a dustbin near the Bataclan concert hall where the bloodiest of the shootings took place.
At least 129 people died in the killings, including 89 at Bataclan. Islamic State has claimed responsibility for the co-ordinated suicide bombings and shootings.
The news came as it emerged that a Belgian fugitive suspected of taking part in the Paris attacks was stopped three times by French police while being driven back to Brussels the following morning but was allowed to carry on his way, a defence lawyer said on Tuesday.
As the manhunt continued for Salah Abdeslam, 26, a lawyer for a friend accused of being his accomplice, and who admits driving Abdeslam home from Paris, told Belgian broadcaster RTBF that a previously reported police check on them as they neared the Belgian border about 9 a.m. on Saturday was only the last of three such occasions when French police halted their car.
As security chiefs looked for missed signals of a plot that French President Francois Hollande says was planned in Belgium and ordered from Syria, Brussels hit back at criticism of its intelligence effort to contain one of the densest collections of radical groups in Europe with ties to Islamic State.
The failure to arrest Abdeslam, identified as the man who rented a Belgian car found near the Bataclan music venue where 89 people were shot dead, has complicated efforts to track down those behind the multiple attacks. French officials said others suspected of direct involvement may also have got away.
Back in Brussels, Abdeslam, whose elder brother Brahim was one of seven attackers who blew themselves up in Paris on Friday night, dropped out of sight.
Such is the concern that he poses a threat to his home city while still at liberty that authorities cancelled a soccer international match against Spain that was to be played on Tuesday.
Friday's France international against Germany, attended by Hollande, was one of the targets of bombers, three of whom, including another man from Brussels, blew themselves up nearby.
Belgium has more than doubled to over 500 the number of troops on its streets, fearing accomplices of those who killed 129 people in total in Paris could strike again in Brussels, the home city of several, including the alleged chief plotter.
With nerves jangling across Europe, German police arrested and then released seven people around Aachen, near the Belgian border, and later cancelled a Germany-Netherlands soccer match in Hanover, evacuating the stadium shortly before kick-off.
Amid a profusion of reported sightings of Abdeslam, RTBF said police pursued a car on the Franco-Belgian border on Tuesday after a witness reported seeing the wanted man among three people in the vehicle.
Police lost it, however, after the Citroen broke through a motorway toll gate and by the time they spotted and stopped it, aided by a helicopter, they found only one occupant. RTBF said police were assessing whether Abdeslam had again eluded them.
Belgian investigators are still questioning the two men charged with terrorism offences whose lawyers say they were unwitting accomplices to Abdeslam when they responded to a call to fetch him from Paris and drive him home early on Saturday.
Prosecutors would not comment on a media report that police had found ammonium nitrate fertilizer -- capable of being used in explosives -- and Kalashnikov bullets at addresses used by the two men: one Mohammed Amri, 27, who drove Abdeslam in his car, and other named in local media as 21-year-old Hamza Attouh.
Amri's lawyer, Xavier Carette, said his client, who works for a homeless charity, knew nothing of any plot and suspected nothing of his friend Abdeslam as they drove back from Paris. Abdeslam had called him two hours after the attacks and said his car had broken down. Amri drove the 280 km (180 miles) to Paris through the night with Attouh to fetch him in his VW Golf.
"You know, when you're on a car journey, you can talk about everything and nothing, listen to music, even smoke a joint, but at no time, No, they didn't talk about that," Carette said.
The fact they were stopped three times by police did not raise his client's suspicions about Abdeslam, he said -- young Arab men got used to that from the police, Carette suggested.
The three men are all from Molenbeek, the Brussels borough that is home to many Muslim immigrant families and is the focus of efforts to unravel how the attacks were planned, funded and supplied. One line of inquiry leads to Abdelhamid Abaaoud, 28, one of more than 350 Belgians who have travelled to fight in Syria and has become a prominent spokesman for Islamic State.
From Molenbeek himself, Abaaoud, who uses the nom de guerre Abu Omar al-Baljiki -- the Belgian -- has boasted of travelling back to Europe under cover and was accused of planning attacks that were foiled in January when police raided a house in the eastern Belgian town of Verviers, killing two young men.
Also this year, he was convicted in absentia of recruiting fighters for Syria. One, local media said, was Abaaoud's own 13-year-old brother. For its population, far more Belgians than any other European nationality have joined in the Syrian war.
Belgian media have said Abaaoud and Salah Abdeslam spent time in prison together for petty offences several years ago.
Abdeslam and his brother Brahim, 31, ran a bar in Molenbeek that was closed down after police found drugs being dealt there over the summer. Public documents show they sold it on Sept. 30.
Family and friends of the brothers, who are French citizens but were born and raised locally, have defended their integrity and were shocked to discover their links to Islamic State, saying they showed little sign of religious belief.
A second man from Brussels, 20-year-old Bilal Hadfi, who blew himself up near the Stade de France stadium, had shown more sign of recent radicalisation, his college history teacher said.
"He was very interested in politics," Sara Stacino told VRT television, recalling a lively student who had changed in the past year, aggressively defending the Islamists who attacked the Paris satirical magazine Charlie Hebdo in January.
"He said it was right, that we had to end freedom of speech, that we had to stop insulting religion," Stacino said. She had written to the school's administrators to raise her concerns about his attitudes but said there was no follow-up.
In the Paris suburbs, police searched a hotel room to the south and a house in the north, rented by the Abdeslam brothers before the attacks. They also impounded another Belgian car found on the streets that French media said had also been rented by the fugitive Salah and might have been used in the attacks.
One group of the assailants on Friday moved around a number of Paris cafes and bars shooting at customers on pavement terraces.
"They were very nice, very kind, correct and well dressed," the woman who rented the brothers the house told Europe 1 radio.
"No robes, no beards. They were people like you and me."
Later on Tuesday, two sources close to the investigation told Reuters that French authorities were now hunting at least one additional gunman after surveillance video showed three men in a car used for the assault on cafes and bars.
As Belgian officials defending their intelligence record pointed out, others among the attackers were based in France, and there were signs those involved had contact with others who have taken part in violence in France before.
Investigators identified a voice in a claim of responsibility from Islamic State as that of French Muslim convert Fabien Clain, 36, from the southwestern city of Toulouse, a source close to the inquiry said.
Le Monde newspaper said Clain, now believed to be in Syria, had been close to Mohamed Merah, who killed seven people in Toulouse in 2012 and is suspected of ordering an attack on a suburban Paris church earlier this year.
Nine people are in custody in France who were close to two of the men who machinegunned the Bataclan music hall during a rock concert, Ismael Omar Mostefai and Samy Amimour.
Other suspects are still being sought. "We're figuring (out) how many there might be," a source close to the investigations told Reuters. Islamic State said eight attackers took part. Seven were killed, of whom five have been formally identified. But word from the investigation sources that a third gunman was being sought over the assault on bars and cafes indicated that there were nine attackers in all.