Asylum-seekers are among those suspected of involvement in violence on New Year's Eve in Cologne, officials said on Friday, intensifying debate about Germany's welcoming of hundreds of thousands of migrants.
Some 121 women are reported to have been robbed, threatened or sexually molested by gangs of men as revelers partied near the city's twin-spired Gothic Cathedral.
The assaults have shaken Germans and prompted ruling parties to promise to crack down on migrants who commit crimes.
Cologne police said they had arrested two males aged 16 and 23 with "North African roots" suspected of involvement in the assaults. A spokeswoman gave no further details.
Separately, Interior Ministry spokesman Tobias Plate told a news conference that federal police had identified 31 people suspected of playing a role in the violence, 18 of whom were in the process of seeking asylum in Germany.
"As of yesterday, the federal police had determined there were 32 criminal acts on the night, with 31 suspects whose names are known," Plate said. "Eighteen had asylum-seeker status."
Plate said most of the 32 criminal acts were tied to theft and bodily injury. Three were related to sexual assaults, and police had not yet identified suspects for these attacks.
Of the 31 suspects, nine were Algerian, eight Moroccan, five Iranian, and four Syrian. Two German citizens, an Iraqi, a Serb and a U.S. citizen were also among those suspected of having committed crimes.
Plate did not say if any of the 31 had been charged. "The investigations are ongoing," he added.
In response to the assaults, Chancellor Angela Merkel's Christian Democrats (CDU) have called for tougher penalties against offending asylum-seekers, according to a draft paper seen by Reuters ahead of a meeting of the party leadership in Mainz.
The paper says those who have been sentenced to prison or probation should be ineligible for asylum.
"Why should German taxpayers pay to imprison foreign criminals?" said Vice Chancellor Sigmar Gabriel, leader of the Social Democrats (SPD), coalition partners to Merkel's conservatives.
"The threat of having to spend time behind bars in their home country is far more of a deterrent than a prison sentence in Germany."
The CDU paper calls for lower barriers to deport criminal asylum seekers, increased video surveillance and the creation of a new criminal offence of physical assault.
The attacks have raised doubts over whether Germany, which took in 1.1 million refugees last year, can succeed in integrating the latest wave and prompted calls for limits on the number of new arrivals.
A new poll for public broadcaster ARD showed Merkel's popularity rising 4 points to 58 percent and support for her conservative bloc up to 39 percent.
Peter Tauber, general secretary of the CDU, rejected the idea of a cap on numbers.
"There are many refugees that are happy to have survived, to have made it here and who are looking for jobs. These people who can contribute to our country are welcome," he told Deutschlandfunk.
"But clearly there are also some who haven't understood what kind of opportunity they've been given."
Julia Kloeckner, leader of the CDU in the state of Rhineland-Palatinate and seen as a possible successor to Merkel, told ZDF television the attacks had been a wake-up call for Germany.
"I think we really need to take off the blinkers," she said.