Updated

Philippine air force planes and helicopters pounded Muslim rebel strongholds Sunday, launching a new offensive against insurgents in the south as the president visited the United States.

President Gloria Macapagal Arroyo (search) authorized airstrikes against "embedded terrorist cells" of the Moro Islamic Liberation Front (search), or MILF, before she left for the United States, where she was scheduled to attend a state dinner in her honor at the White House, officials said.

The MILF is blamed for a series of recent bombings and other attacks in the southern Mindanao region.

The rebels have denied involvement in the recent attacks, but MILF spokesman Eid Kabalu said they would fight back if the army launched a new offensive.

Gen. Narciso Abaya, the military chief of staff, said the assaults target selected strongholds of the separatist group in Mindanao, where suspected assailants have fled following bombings and attacks that have left more than 210 people dead this year.

"These are MILF camps in Mindanao where attackers take refuge, rest and get their logistics after committing atrocities," Abaya told radio station DZMM.

The head of the military's Southern Command in Zamboanga, Lt. Gen. Roy Kyamko, told a news conference that planes dropped six 250-pound bombs on MILF strongholds along the mountainous boundary of southern Lanao del Sur and Lanao del Norte provinces. Helicopters fired rockets at rebel positions there, military officials said.

Following the airstrikes, ground forces moved in, backed by artillery fire, Kyamko said.

Intercepted rebel radio messages indicated scores of rebels were killed in the airstrikes, army Maj. Gen. Cristolito Balaoing said.

Kabalu, however, disputed the military claims, saying MILF field commanders have not reported any deaths.

An estimated 50 Muslim guerrillas have been killed on three southern fronts since Arroyo announced the new crackdown.

Hundreds of soldiers were being deployed from elsewhere in the country to reinforce three army divisions involved in the ongoing offensive, Kyamko said.

Arroyo has demanded that the MILF renounce terrorism and surrender rebels responsible for the recent attacks by June 1 or it will be declared a terrorist organization -- a step toward cutting off the rebels' international support.

Aside from the MILF, the military also is engaging Al Qaeda-linked Abu Sayyaf (search) Muslim rebels on southern Jolo island and communist guerrillas scattered on Mindanao.

Arroyo will be the guest of honor at a state dinner Monday in Washington hosted by President Bush. She is expected to seek an increase in U.S. military aid and discuss a new bilateral counterterrorism exercise this year in Mindanao.