Philippine troops have rescued a Roman Catholic priest and another civilian who were among dozens of people abducted in May when hundreds of militants aligned with the Islamic State group laid siege on southern Marawi city, officials said Sunday.

Presidential adviser Jesus Dureza and two senior security officials said without elaborating that troops retrieved the two late Saturday after a battle to recapture a key mosque and another Islamic building used as a command center by the gunmen in Marawi.

The two security officials spoke on condition of anonymity because they were not authorized to publicly disclose details about the ongoing assaults. The government refused to comment on the reported rescue of the hostages, saying ongoing assaults may be jeopardized and troops and other hostages may be endangered if it releases details.

At least 860 people, including more than 660 militants and 147 troops and police, have been killed since the siege began in Marawi, regarded as a center of Islamic faith in the southern third of the largely Roman Catholic nation. Marawi's central business district and outlying communities now resemble a smoldering wasteland of disfigured buildings and houses.

The siege has sparked fears that the Islamic State group may gain a foothold in Southeast Asia by influencing and providing funds to local militants as it suffers battle defeats in Syria and Iraq. The United States and Australia have deployed surveillance aircraft to help Filipino troops battling the Marawi attackers.

An army commander, Col. Romeo Brawner, said Sunday in a news conference in Marawi that troops were battling to eradicate up to 80 remaining militants who may be holding more than 40 hostages. With fewer fighters, the militants have forced some of their hostages to join the fighting and have resorted to improvised bombs and booby traps to slow the military advance, he said.

At least two militant leaders, Isnilon Hapilon and Omarkhayam Maute, were believed to still be with the gunmen in Marawi, Brawner said.

"It's very important that we get their leaders so there will be no repeat of what happened in Marawi. We do not want this kind of terrorism to flourish or expand," he said.

Father Teresito Soganub was last seen in May in a video, apparently taken under duress by the militants, where he said he was with about 200 other hostages and that his captors wanted the military to withdraw its forces from Marawi.

About 600 militants, waving Islamic State-style black flags, seized commercial buildings, mosque and houses in the city's central business district on May 23 after an army-led assault failed to get Hapilon and other militant leaders in a safe house in the mosque-studded city.

"We want to live another day; we want to live another month," Soganub said in the video while standing alone in front of debris and partially burned buildings.

The large number of militants and their array of weapons surprised President Rodrigo Duterte, who declared martial law in the south to deal with the Marawi crisis, the worst he has faced so far.

Troops battled the scattered militants for five hours Saturday to wrestle back control of the Bato mosque and a nearby Islamic foundation center, military spokesman Col. Edgard Arevalo said.

Military chief of staff Gen. Eduardo Ano described the seizure of the mosque as an "enormous" military gain because it served as a battle command center of the militants.

"The Armed Forces of the Philippines will press on relentlessly until conclusion," Ano said. "We urge the remaining terrorists, especially former hostages turned fighters, to ... surrender while they still have time," Ano said.

While the military presses airstrikes and ground assaults, the government has started to build temporary shelters for some of the hundreds of thousands of residents displaced by the siege. Defense Secretary Delfin Lorenzana estimated that it would take more than 50 billion pesos ($1 billion) to rebuild Marawi, a scenic lakeside city of about 200,000 people before the siege.