* Residents see at least 100 bodies in war zone, says politician
* A cousin of Maute brothers, leaders of Marawi siege, arrested
* Police say arrested man is a suspected bomber (Adds military clarification that arrested militant is a cousin, not brother of the Mautes)
By Neil Jerome Morales and Simon Lewis
MARAWI CITY, Philippines, June 15 (Reuters) - A Philippines politician said on Thursday residents fleeing besieged Marawi City had seen scores of dead bodies in an area where intense fighting has taken place between security forces and Islamist militants over the past three weeks.
"Dead bodies, at least 100, scattered around the encounter area," Zia Alonto Adiong, a politician in the area who is helping in rescue and relief efforts, told reporters, referring to accounts he had received from fleeing residents.
The military said it could not confirm the report.
The army has said 290 people have been killed in the more than three weeks of fighting, including 206 militants, 58 soldiers and 26 civilians.
Lieutenant Colonel Jo-Ar Herrera, a military spokesman, said troops were advancing toward the commercial centre of Marawi City, which is held by the militants who have sworn allegiance to Islamic State.
"We intend to finish the fight as soon as possible. Our tactical commanders are doing their best," Herrera said.
But troops still faced up to 200 fighters, many of whom had taken up sniper positions, he said.
"The battlefield is very fluid," he said.
Earlier, the military said it had arrested a cousin of the top militant commanders leading the Islamists in their fight against the government.
The man, Mohammad Noaim Maute, alias Abu Jadid, was arrested at a checkpoint near the coastal city of Cagayan de Oro just after dawn, Herrera said.
Herrera had earlier identified him as a brother of Omarkhayam and Abdullah Maute, who head the Maute gang that is at the forefront of the battle for Marawi City.
Marawi is about 100 km (60 miles) south of Cagayan de Oro, but it was not clear whether Mohammad was coming from the embattled city.
Most of the seven Maute brothers, including Omarkhayam and Abdullah, are believed to be in Marawi.
Their parents were taken into custody last week in separate cities.
Brigadier-General Gilbert Gapay, spokesman for the military's Eastern Mindanao Command, said Mohammad Noaim Maute was a suspected bomb-maker for the group.
He said Maute was holding a fake student card of the Mindanao State University, based in Marawi, when stopped at the checkpoint. He was not armed.
Police said Maute, an Arabic-language teacher, readily admitted his identity when questioned. (Additional reporting by Manny Mogato; Writing by Raju Gopalakrishnan; Editing by Robert Birsel)
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