MANILA - The United States has expressed its continued support in the country's counter-terrorism efforts including offensives in conflict-stricken Marawi City, vowing to back the Philippine military in quelling extremists.

The Philippines' closest defense ally would continue to coordinate with the Armed Forces of the Philippines (AFP) in enhancing counter-terror programs for both countries, US Ambassador to the Philippines Sung Kim said Tuesday.

"In any context, counter-terrorism requires cooperation. It's very difficult for a single country to deal effectively with terrorism we face around the globe. We will continue to work with the AFP," Kim said in a press conference in Camp Aguinaldo.

"You're seeing [the] situation in Marawi where our small contingent was there as requested by the Philippine government... really providing very important assistance in terms of intelligence sharing, information sharing, and technical advise," he added.

Since the Marawi crisis broke out on May 23, US troops have been providing technical assistance to Filipino soldiers battling Islamic State-inspired extremists.

Defense Secretary Delfin Lorenzana said the Marawi situation is "a class by itself" in terms of terror activities, and admitted that they are still puzzled as to how hundreds of terrorists were able to sneak into Marawi unnoticed.

The conflict has been raging on for four months, leaving the once bustling urban and cultural capital in ruins, displacing more than 200,000 residents, and killing more than 800, most of them terrorists.

"We have not yet found out how they got in, a lot of them coming from other places" he said.

Lorenzana and Kim noted that one of the latest efforts to enhance both countries' counter-terrorism programs was the successful staging of Tempest Wind, a joint counter-terror drill designed to test the ability of both governments to conduct anti-terrorism operations.

During the drill, troops simulated response to an airplane hijacking by elements of the Islamic State.

Kim said the US would be ready to help when called to assist if and when hijacking of such nature occurs in the Philippines.

"We are close allies and friends with the Philippines, if requested by the Philippine government to provide assistance, we will be there to provide that type of assistance," Kim said.

Apart from military assistance, the US has given P730 million in aid for relief and rehabilitation efforts in Marawi City.

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