The Philippines army said it captured an important rebel base
The Philippines army says it has captured a top Muslim rebel, Camarudin Hadji Ali, a claim denied by the Moro Islamic Liberation Front (MILF).
The military claim came after days of fighting between the army and another rebel group, Abu Sayyaf, in which more than 30 rebels were killed.
At least eight marines were also killed in the fighting, on Jolo island.
The army has been trying to crush rebels as efforts at peace talks with Muslim separatists have faltered.
"Ali is a leader of the MILF's 105th Base Command under Ameril Umbrakato, who are both wanted for a series of deadly attacks last year in Mindanao," regional army spokesman Colonel Jonathan Ponce said.
He said Camarudin Hadji Ali, also known as Commander Mudi, was picked up at his wife's home in Cotabato City, on Mindanao, which was under surveillance by the police and military.
However MILF spokesman Eid Kabalu has denied that any senior MILF field operative had been arrested.
"The military arrested the wrong person," he told AFP news agency, adding that Muslim civilians had informed the group that a man with a similar name had been arrested.
Mr Umbrakato and another MILF field commander were accused of breaking a five-year-old ceasefire last year.
More than 300 people have been killed and up to 750,000 displaced in fresh fighting.
The government and MILF have agreed to create a panel of international brokers to help facilitate a new attempt at peace talks.
But since the weekend, fighting has been heavy in areas of the south where another rebel group, Abu Sayyaf, is based.
Lieutenant-General Ben Dolorfino, commander of military forces in the southern Philippines, told reporters that at least 34 Abu Sayyaf militants have been killed since Sunday, when troops, backed by air strikes, assaulted a fortified rebel base in the hilly interior of the southern island of Jolo.
On Monday, about 100 Abu Sayyaf fighters ambushed a military convoy in Indanan town, on Jolo.
In that deadly encounter, 15 of the 34 Abu Sayyaf were killed while eight soldiers were killed and nine wounded.
Lt Gen Dolorfino described the capture of Indanan town as a major strategic achievement.
Jolo is the stronghold of the Abu Sayyaf rebels, one of the smallest but deadliest Islamist militant groups in the largely Roman Catholic Philippines.
Established in the early 1990s, it has kidnapped dozens of foreign aid workers, missionaries and tourists in the south and was blamed for the country's worst terrorist strike, the bombing of a ferry in 2004 that killed more than 100 people.
Earlier this month, officials claimed the capture of two other high-profile militants - Hajer Sailani, an alleged member of Abu Sayyaf, and Dino-Amor Rosalejos Pareja, the leader of the deadly Rajah Solaiman group of Christian converts to Islam.
The United States keeps about 500 soldiers in the south, assisting Philippine soldiers with intelligence, equipment and training.