MANILA — Malaysian security forces killed 31 Filipino gunmen on the island of Borneo, officials said Thursday, and the government rejected calls by the United Nations for an end to the fighting. At least 60 people, including eight Malaysian police officers, have been killed in the nearly monthlong conflict over an effort by followers of a Philippine-based sultan to assert a historical claim over parts of Borneo Island. “The secretary general is closely following the situation in Sabah, Malaysia,” said a statement from the United Nations released on Wednesday. “He urges an end to the violence and encourages dialogue among all the parties for a peaceful resolution of the situation.” A spokesman for Jamalul Kiram III, the leader of the group fighting in the Malaysian state of Sabah, said the sultanate was declaring a unilateral cease-fire in reaction to the call by the United Nations. He said an order was given for the group to take a “defensive position” and not to engage Malaysian troops. “Malaysia, reciprocate the call for the cease-fire,” the spokesman, Abraham Idjirani, appealed at a Thursday afternoon news briefing. The Malaysian defense minister, Ahmad Zahid, rejected the calls by the United Nations and the sultanate. “A unilateral cease-fire is not accepted by Malaysia unless the militants surrender unconditionally,” he said in a statement, adding later: “Don’t believe the cease-fire offer by Jamalul Kiram. In the interest of Sabahans and all Malaysians, wipe out all the militants first.” Prime Minister Najib Razak of Malaysia told reporters on Thursday afternoon that the Philippine president, Benigno S. Aquino III, had telephoned him after the United Nations statement to get his reaction. “I informed President Aquino that they need to surrender unconditionally and their weapons have to be handed over to us,” he said during a visit to Lahad Datu, the area where much of the fighting has taken place. Malaysian officials have called for the extradition to Malaysia of the group’s leader in Manila. Mr. Aquino said Thursday that criminal charges were being prepared against the sultan by the country’s National Bureau of Investigation, and he rejected calls for an immediate extradition. The Philippines and Malaysia do not have an extradition treaty, but they have a mutual legal assistance agreement that facilitates the capture and repatriation of fugitives. “Let our citizens here in the country face the charges that we will be proffering,” Mr. Aquino said. “Then we will talk about other developments after they have satisfied the requirements of our laws.” The situation began in mid-February, when about 200 people from the southern Philippines arrived in a remote coastal area of eastern Malaysia and announced that they were members of a royal army in service of the Sultanate of Sulu, which ruled the southern Philippines and parts of Sabah for centuries. The group was initially received peacefully, but after multiple requests that they return to the Philippines, violence broke out. The Malaysian authorities carried out several assaults against the group, using fighter jets, mortars and several battalions of ground troops. Militant leaders in the Philippines have said that fighters from the restive southern part of the country would try to make their way to Sabah to act as reinforcements for the outnumbered Filipino fighters. Malaysian and Philippine navy ships are patrolling the waters between the two countries to stop further incursions.