Malaysia is boosting security in Sabah state amid an increasingly tense confrontation with a group from the Philippines occupying a village there.
Nearly 200 Filipinos landed by boat in Lahad Datu last month, saying the land belongs to their sultan.
The initially peaceful stand-off erupted on Friday in clashes which left eight policemen and 19 Filipinos dead.
Philippines President Benigno Aquino has called for calm and has sent his foreign minister to Malaysia.
Malaysia Prime Minister Najib Razak, who has come under domestic pressure to bring an end to the incursion, said he had dispatched two additional battalions to Sabah, on Borneo island, Malaysia's Bernama state news agency reported.
Mr Najib said at the weekend that security forces were authorised to "take any action deemed necessary" against the intruders.
Meanwhile Manila said that Foreign Secretary Albert del Rosario would also ask for permission for a Philippines ship carrying aid and consular help to be allowed to reach the intruders and evacuate the wounded.
Sabah police chief Hamza Taib said the additional troops would boost public confidence, and would work alongside local police, AFP news agency reports.
But on Monday, Mr Aquino said it was "not reasonable to ask for understanding if you are pointing a gun at the face of who you are speaking to".
A reasonable conversation will only begin once you are ready to calm down and restrain yourselves, and to face the table with an open mind," he said.
The Filipinos were led into the region in early February by Agbimuddin Kiram, who is the younger brother of the self-proclaimed Sultan of Sulu Jamalul Kiram III.
The Sulu Sultanate once spread over several southern Philippine islands as well as parts of Borneo, and claimed Sabah as its own before it was designated a British protectorate in the 1800s.
Sabah became part of Malaysia in 1963, and the country still pays a token rent to the Sulu Sultanate each year.
The Royal Army of Sulu wants Malaysia to recognise it as the rightful owner of Sabah, and to renegotiate the terms of the old lease - something Malaysia has made clear it has no intention of doing.
On Friday, violence broke out as security forces apparently neared the clan's base, but the exact details remain unclear, with each side accusing the other of opening fire.
On Sunday, three police officers were killed in clashes in Semporna, south of Lahad Datu. It was unclear whether the incidents were connected, but it has added to concerns the situation could escalate.
Residents of Semporna are reported to be fleeing the area, telling AFP that bodies were lying in the streets and that they feared more violence.
"Our peaceful town has become a nightmare to live in," one resident was quoted as saying,
"We are moving out because these are uncertain times. We heard the gunshots. My children are afraid."
The Associated Press reported that Filipino residents in Sabah province had fled to the southern Philippines to escape the violence.