(CNN) -- A Philippine clan leader's bizarre attempt to revive the territorial claims of a defunct Islamic sultanate on the island of Borneo appears to be falling apart.
With his followers engaged in a deadly game of cat and mouse with Malaysian security forces in the villages and palm oil plantations of northeastern Borneo, the self-proclaimed Sultan of Sulu is calling for a cease-fire after the U.N. secretary-general urged an end to the violence.
But Malaysia promptly rejected the proposal and said its security forces had killed more than 30 of the Filipino fighters on Thursday.
Between 100 and 300 men from the southern Philippines came ashore in the area, in the Malaysian state of Sabah, about three weeks ago, claiming to be the Royal Army of the Sultanate of Sulu, a former kingdom in the region whose power has faded.
Jamalul Kiram III, one of the clan leaders claiming to be the rightful sultan, says he sent the men, some of whom are armed, to Sabah to reassert the sultanate's sovereignty over the area.
But their arrival in the coastal district of Lahad Datu caused alarm and embarrassment in Malaysia, which still pays a token fee each year to the sultanate for the lease of Sabah.
While scrambling to explain how so many armed intruders had managed to slip through the maritime border that separates Sabah from the nearby southern Philippine islands, Malaysian security forces tried to persuade the clansmen to return home peacefully.
But those efforts -- supported by the Philippine government, which is pursuing a peace initiative with Muslim rebels in its restive southern islands -- failed as clashes in Sabah late last week left about 28 people dead, including several Malaysian police officers.
A Malaysian offensive
Malaysian authorities responded by launching an offensive using fighter jets, mortar shells and ground troops on Tuesday. They followed that up with what they called a "mopping up" operation, going house to house in the area, searching for the Filipino fighters.
But Kiram's spokesman, Abraham Idjirani, said Wednesday that the Malaysian attack had missed its target, striking an area that the Filipino clansmen had already vacated. He claimed the group hadn't suffered casualties.
A day later, Idjirani made the call for a cease-fire on behalf of Kiram, saying the clan was responding to U.N. Secretary-General Ban Ki-moon's plea for the fighting to stop.
But Malaysian Prime Minister Najib Razak said Kuala Lumpur won't consider any request for a cease-fire as long as the armed intruders in Sabah refuse to lay down weapons unconditionally, the official news agency Bernama reported Thursday.
Later on, Ismail Omar, the head of the Malaysian Police, said security forces had killed 32 "militants" in Sabah on Thursday, including one they believed had the rank of general, according to Bernama.
The task of the Malaysian security forces in hunting down the clan members has been made more complicated by the strong ethnic ties between many of the people in Sabah and the southern Philippines. Many of the sultanate's followers are believed to have friends and family living in the area.
Malaysian police have admitted that the Filipinos are blending in with the local population.
In a statement Wednesday, Ban's office said the U.N. secretary-general "urges an end to the violence and encourages dialogue among all the parties for a peaceful resolution of the situation."
Ban also expressed concern about the effects of the fighting on the civilian population in the area, including migrants.
People and goods regularly go back and forth across the porous sea border between Sabah and the southern Philippines.
Established in the 15th century, the Sultanate of Sulu became an Islamic power center in the southern Philippines that at one point claimed sovereignty over Sabah.
But the encroachment of Western colonial powers, followed by the emergence of the Philippines and Malaysia as independent nation states, steadily eroded the sultanate's influence. Sulu is now a province within the Republic of the Philippines.
But the historical connection still fuels tensions between Malaysia and the Philippines, with Manila retaining a "dormant claim" to Sabah through the Sultanate of Sulu, according to the CIA World Factbook.
The Philippines claims much of the eastern part of Sabah, which was leased to the British North Borneo Company in 1878 by the Sultanate of Sulu. In 1963, Britain transferred Sabah to Malaysia, a move that the sultanate claimed was a breach of the 1878 deal.
CNN's Karen Smith contributed to this report.