The Philippine military said Friday only about 60 pro-Daesh militants are still fighting in a two-month siege of southern Marawi city that has left 630 people dead and swaths of the region in ruins.

Military spokesman Brig. Gen. Restituto Padilla said most of the militants' leaders are believed to be still with the main group of gunmen fighting in an area less than one square kilometer (0.4 square mile). Despite the militants' setbacks, officials still are unable to say when the violence will end.

"Our troops are in a very high state of morale, all leaning forward to finish this operation at the soonest time possible," Padilla said in a news conference in Manila.

President Rodrigo Duterte has said he ordered troops to refrain from staging a massive assault to ensure the safety of hostages still held by the gunmen, possibly in a mosque. As of the 67th day of fighting, 471 militants, 114 troops and police and 45 civilians have been killed, according to the military.

"We believe their leadership is still there. That may be the reason why they're intently guarding some areas," Padilla said.

Congress has approved Duterte's request to extend a 60-day declaration of martial law to the end of the year to allow troops and police to prevent other rebel groups from reinforcing the militants in Marawi.

On Tuesday, 59 men suspected of being on their way to help the militants were arrested in southern Ipil town and Zamboanga city. The suspects were flown Friday under heavy guard to the Department of Justice in Manila, where they denied before prosecutors that they were aiming to back up the extremists.