The Philippine military has found the bodies of 18 civilians who were gunned down by Muslim militants in the ongoing fight for the control of southern Marawi city.

Military spokesman Brigadier General Restituto Padilla says the dead include a group of four men, three women and a child who were found near a road close to the Mindanao State University in Marawi.

Police say eight other men were fatally shot and thrown in a shallow ravine along a highway, just 200 metres away from a military checkpoint in the city. A paper sign attached to one of the men said “monafiq”, which means traitor.

“The hands of some of the victims were tied behind their backs, and most of them were shot in the head,” police officer Jamael Mangadang of a security task force, told reporters.

Padilla says 61 militants have been killed together with 13 soldiers and four police officers since Tuesday, when a failed raid to capture one of Asia’s top militants triggered an attack on the city.

More than 2200 people are estimated to be trapped in the conflict zone in Marawi, fearing for their lives from threats of Islamist militants and military air strikes.

Residents have been sending appeals for help via text message, but rescue teams have not been able to penetrate the districts where they are located, said Zia Alonto Adiong, spokesman for the local province of Lanao Del Sur.

“The number is still continuing to rise,” he said. “They are asking for help to extract them or send relief goods.”

Mr Adiong said local officials were seeking clearance from the military to send rescue teams to 25 districts where the trapped residents were located.

To those trapped, he said: “Go to the safest areas of your houses, lock your doors, do not let anyone enter your homes and wait for us.”

The battles with the Maute group, which has pledged allegiance to Islamic State, started on Tuesday during a failed raid by security forces on one of the group’s hideouts that spiralled into chaos.

Fierce battles restarted on Sunday as ground troops engaged Maute fighters with heavy gunfire. Plumes of smoke were seen on the horizon and helicopters fired at least eight rockets on rebel positions.

A surveillance drone circled the sky above Marawi City. Some civilians left on foot, others were seen tying white cloths to poles to distinguish themselves from militants as soldiers huddled behind armoured vehicles slowly advanced.

An ambulance was seen speeding away from the fighting and soldiers said a captured militant was inside.

Tens of thousands of people have fled Marawi since Tuesday, when militants went on the rampage seizing a school, a hospital, and a cathedral.

President Rodrigo Duterte has declared martial law in the southern region of Mindanao.

Who are the Maute?

• The Maute are an armed Muslim group that’s pledged allegiance to Islamic State
• Hapilon is reportedly the leader of the alliance
• The Maute has been blamed for a bomb attack that killed 15 people in southern Davao city, Duterte’s hometown, last September
• Last month, troops killed dozens of Maute militants and captured their jungle camp near Lanao del Sur’s Piagapo town
• Troops found homemade bombs, grenades, combat uniforms and passports of suspected Indonesian militants in the camp, the military said