MARAWI CITY, Philippines (Reuters) - The Philippines is preparing to declare the end of fighting in a southern city seized for five months by pro-Islamic State rebels, a top military commander said on Saturday, as troops continued a phased withdrawal from the devastated lakeside city.   Only 20 insurgents remained in a small area in Marawi City, including five  significant  figures, and three battalions of troops were closing in on their positions, said Lieutenant-General Carlito Galvez.     Most probably tomorrow, we can do it,  Galvez told reporters when asked when the military can declare fighting is over.  We can declare it is totally complete.    Galvez said troops are zeroing in on three sons of Isnilon Hapilon, the slain  emir  of Islamic State in Southeast Asia, and two Malaysians, including Amin Baco, who has been central to facilitating the movement of foreign fighters in the region.   We cannot say our mission is totally accomplished or completed if the five persons are still there,  he said, adding the remaining militants are  struggling to survive  and to protect their shrinking position.   Another general told Reuters they were also looking for a prominent Indonesian militant. The military is concerned Hapilon s sons and these foreign fighters could succeed core leaders of the alliance killed this week.    Hapilon and Omarkhayam Maute were killed by commandoes on Monday. Malaysian Mahmud Ahmad, who experts say may have funded the Marawi siege, was also dead, according to a freed hostage, but his body has yet to be found. The defense ministry said on Saturday that forensic tests by the U.S. Federal Bureau of Investigation had confirmed that the man killed was Hapilon. The United States has provided technical support to treaty ally the Philippines, including surveillance drones. The deaths of the leaders could slow down any effort by Islamic State to establish a presence in Mindanao, a vast island with a history of rebellion and home to the predominantly Roman Catholic nation s Muslim minority.  The organization and combat capability of the rebels has stunned the military. Some experts see the siege as a prelude to a more ambitious bid by Islamic State loyalists to exploit Mindanao s poverty and use its jungles and mountains as a base to train, recruit and launch attacks in the region. Galvez, head of the Western Mindanao Command, inspected troops in Marawi and sent off a battalion of marines central to  military operations . It was the second unit to leave the conflict area.   The military declined to divulge the number of troops remaining in Marawi. Elite commandoes were leading the assault, with army infantry battalions and police commandoes securing safe areas.   The military said eleven hostages were  processed  on Saturday to determine whether they were really captives or militant members and sympathizers trying to slip away.   Galvez said rehabilitation, including retrieval of the dead, would start after the end of hostilities is declared. The Philippines estimates the rebuilding of areas battered by months of government air strikes could cost at least 50 billion Philippine pesos ($971 million). 