International monitors said the fighting itself could affect the crash site, underlining the growing complexity of trying to establish who shot down Malaysia Airlines flight MH17.
In Donetsk, Alexander Hug, deputy head for the Organization for Security and Cooperation in Europe's monitoring mission in Ukraine, said monitors would not visit the site on Sunday.
"The situation on the ground appears to be unsafe ... we therefore decided to deploy tomorrow morning,'' Hug, flanked by Dutch and Australian experts, told reporters. "Fighting in the area will most likely affect (the) crash site,'' Hug said.
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An OSCE spokesman said the group would try again on Monday.
The separatists are still in control of the area where the plane was shot down earlier this month but fighting in the wider eastern regions of Donetsk and Luhansk has been heavy as Ukrainian government forces try to drive them out.
It was raging in at least five places on Sunday and Donetsk region health officials said 13 people were killed in fighting in the town of Horlivka, known as Gorlovka in Russian.
Lysenko said troops were advancing east from the town of Makievka towards Shakhtarsk, around 25 km (16 miles) from the crash site. Shakhtarsk residents said air strikes hit the town.
"Our military is advancing, fighting goes on every day, every night, they have already liberated two-thirds of the territory,'' Lysenko told a news conference in Kiev.
But Ukrainian Foreign Minister Pvalo Klimkin said the Ukrainian army was respecting a no-fight zone within 20 kilometres from the site.
The Russian foreign ministry said Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry had agreed on the need to ensure a swift ceasefire in what it described as an "internal conflict''.
Earlier, Malaysian Prime Minister Najib Razak said an agreement reached with separatist leader Borodai would "provide protection for international crash investigators'' to recover human remains and ascertain the cause of the crash.
The OSCE has provided a team to monitor the site in advance of an investigation, but Najib said a full team of investigators was needed to ensure any human remains left there were removed.
"We also need a full deployment of investigators to have unfettered access to the crash site so we can understand precisely what happened to MH17. I hope that this agreement with Mr Borodai will ensure security on the ground, so the international investigators can conduct their work,'' he said.
"Three grieving nations'', Malaysia, Australia and the Netherlands, had formed a police group to secure the site, he said in a statement issued by his office. The Netherlands and Australia said the mission would not be armed.
Among the 298 people who died aboard the Boeing 777 on its flight from Amsterdam to Kuala Lumpur on July 17 were 193 Dutch nationals, 43 Malaysians and 28 Australians.
Malaysian experts have said they believe at least 30 investigators will be required to cover the full site of the crash, in addition to Dutch investigators and an expert from the United Nations' civil aviation body, the ICAO.
In the Australian capital Canberra, Prime Minister Tony Abbott said an unarmed police mission led by the Netherlands and made up of about 49 officers would travel to the site. Officials said a total of 170 Australian police were deployed in Ukraine.
Abbott, who has played a leading role in pressing for an investigation, told reporters the force would probably stay no longer than three weeks. "Our objective is to get in, to get cracking and to get out,'' he said.