The Philippine military is fighting the pro-"Islamic State" (IS) Maute group using a combination of ground troops and airstrikes from helicopters as it tries to flush militants out of buildings and drive them from the southern city of Marawi where they have been fighting government forces for four weeks.

A number of Maute fighters have reportedly slipped out of Marawi either to seek medical treatment or to escape arrest. At the same time, the government fears the Maute group is seeking to expand its area of activities.

Conflict began on May 23 after the Maute group captured Marawi and raised IS flags on buildings, prompting President Rodrigo Duterte to impose Martial Law on the island province of Mindanao. More than 300 people have died since the start of the conflict.

"There is a possibility that one or two Maute fighters have slipped out of Marawi, but it is not happening on a large scale," Restituto Padilla, a spokesperson for the Armed Forces of the Philippines (AFP), told reporters on Monday.

But security analyst and military historian Jose Antonio Custodio said the arrests indicate that Maute fighters are fleeing the area.

Read: Duterte's real motives behind imposing Philippine martial law

Civilians trapped in conflict

On Wednesday, Philippine authorities said Islamist militants raided a school in a village 160 kilometers (100 miles) from Marawi. According to the latest media reports, the militants took over 30 hostages before fleeing after a day-long battle with government forces. The hostages were freed and there were no reports of any casualties.

According to reports, the attack was carried out by members of the Bangsamoro Islamic Freedom Fighters (BIFF), another Islamist group in the southern Philippines that have pledged allegiance to IS.

Padilla said at a news conference that is was possible the attack by BIFF could have been a diversion from the offensive in Marawi against Maute fighters.

"If this is a diversionary move, it's not the first by these BIFF gunmen," Padilla said.

Read: IS-hit Marawi celebrates tearful Philippines Independence Day

In Marawi, more than 200,000 residents have reportedly fled to neighboring municipalities when violence broke out. They moved in with friends or family or squeezed into covered courts and madrasas converted into makeshift evacuation centers. Health authorities have reported that illnesses, typical in congested areas, like dehydration and skin diseases are rampant.

But advocates and rights groups are more anxious about the safety and well-being of the estimated 300-500 civilians who remain trapped in corners of the city center that the Maute rebels continue to control.

More than 900 people have been rescued by rescue teams and the military but some remain cut off in areas that are in the line of sniper fire and have been declared as no-go zones.

The Department of Social Welfare and Development (DSWD) has not been able to access the areas where fighting continues.

"There is no food and no water for those trapped in Marawi," Samira Gutoc, head of the Ranao Rescue Team told DW. "We are asking the military and the Maute to let food in."

The displaced residents have also called for a stop to the air strikes that have pulverized their homes almost every day since the skirmishes began.

Military cooperation amid growing threat

Meanwhile, the Philippines, Malaysia and Indonesia have launched joint naval patrols to safeguard porous borders and maintain stability in the region.

 According to a statement the cooperation is in response to threats such as "piracy, kidnapping, terrorism and other transnational crimes in regional waters."

The threat of terror cells in Southeast Asia by groups pledging allegiance to IS is growing as the group's loses footing in the Middle East.

The presence of foreign fighters among the Maute rebels also alarmed the government who talked about a new kind of hybrid terrorist that is also engaged in criminality and illegal drug running apart from terrorist acts.

Duterte's declaration of Martial Law in Mindanao was challenged by the Church and opposition groups who filed a complaint with the Supreme Court.

Duterte announced that he would withdraw the troops from Marawi if the Supreme Court invalidates his declaration of Martial Law, but the AFP holds a different view.

"Offensives will continue because there's a threat that's being faced. And it would be foolhardy to stop the fight because the martial law was lifted. If there's a threat to public safety, the offensives will continue," said AFP spokesperson Padilla.