Malaysian police said on Friday they had arrested more than 50 people in a remote state for suspected links to a nearly month-long incursion by armed Filipino Islamists.
Clashes between the gunmen and its security forces have left 60 people dead, and Malaysia has rejected a call by the fighters' leader for a ceasefire in a farming region where the militants are being pursued.
In announcing the arrests, federal police chief Ismail Omar said they had all occurred in other areas of the state of Sabah, outside the battle zone where the militants and armed forces were facing off.
"Outside the operation area, police already arrested certain suspects who we believe have links to the invaders," Ismail said.
He said more than 50 had been arrested, including men and women. He declined to give any further details such as whether they were foreigners or Malaysians.
Scores of followers of a self-proclaimed Philippine sultan landed in the state on Borneo island last month to assert a long-dormant territorial claim in what has become Malaysia's worst security crisis in years.
The main group of militants was holed up in a sleepy farming village for three weeks until two deadly shootouts with security forces last weekend triggered a military assault that scattered them amid vast oil palm plantations.
However, there have been reports of other gunmen elsewhere along Sabah's coast, raising fears of a wider infiltration by fighters and the possibility they may have been aided by sympathisers already in Malaysia.
The Philippines, meanwhile, said it had formally asked Malaysia to ensure humanitarian treatment for 10 Filipinos who it says have been captured.
The government of President Benigno Aquino said previously that Malaysia had informed Manila that 10 Filipinos had been captured. Malaysia has not confirmed that account.
"Today, we have asked the Malaysian government to treat our people under their custody humanely," Aquino's spokesman Edwin Lacierda told reporters.
"We expect and we have already informed the Malaysian embassy that our Philippine embassy team (in Sabah) be given full access to the Filipinos."
The incursion was carried out by a group of followers of Jamalul Kiram III, the self-proclaimed heir to the former southern Philippine sultanate of Sulu, which had a historical claim to Sabah.
Kiram's people say about 235 people took part in the incursion, and they also claim that 10 had been captured.
Ismail said he had no knowledge of the captives. Malaysian authorities have continually issued only sketchy information on the crisis, citing security reasons.
Ismail said the arrests were made under the Security Offences (Special Measures) Act, a new law introduced to replace a tough British colonial-era law as part of a reform drive.
But the new act has come under criticism for giving authorities too much power to hold people on broad grounds. London-based Amnesty International has called it "deeply flawed".