The top US and Pakistani military leaders met in Spain to discuss ways to shore up strained ties after a US raid that killed Al-Qaeda leader Osama bin Laden, according to a Pentagon spokesman.

Joint Chiefs of Staff Chairman Mike Mullen and his Pakistani counterpart General Ashfaq Kayani sat down for more than two hours of talks late Friday on the sidelines of a NATO conference in Seville, Mullen's spokesman Captain John Kirby told AFP.

"They agreed that the relationship between our two countries remained vital to the region and that both sides had taken positive steps to improve that relationship over the past few months," Kirby said.

"They also discussed the state of military-to-military cooperation and pledged to continue to find ways to make it better."

It was the first meeting between the pair since the May 2 nighttime military raid in which US Navy Seals, without first notifying Islamabad, killed the Al-Qaeda leader in the compound in Abbottabad where he had been hiding.

As relations worsened in the aftermath of the raid, Washington announced that it could cut some of the $2.7 billion in military aid it sends to Pakistan.

Islamabad, for its part, ordered as many as 200 US military trainers out of the country in the aftermath of the operation.

US Defense Secretary Leon Panetta has expressed frustration that Islamabad has so far failed to crack down on Haqqani network militants that Washington suspects attacked the US embassy and NATO headquarters in Kabul on September 13-14.

Echoing his comments, Mullen also expressed "deep concerns about the increasing -- and increasingly brazen -- activities of the Haqqani network and restated his strong desire to see the Pakistani military take action against them and their safe havens in North Waziristan," said Kirby.

His comments came after the US ambassador in Islamabad cited evidence linking the Pakistani government with the Taliban-allied Haqqani network.

In blunt comments broadcast by state-run Radio Pakistan, ambassador Cameron Munter said the Kabul attack "was the work of the Haqqani network."

"This is something that must stop," he added.

Panetta has also warned that the United States would retaliate against Pakistan-based insurgents.

While relations are frayed, Pakistan is seen as key for US military operations in Afghanistan, where the United States is to trying to beat down a resilient Taliban insurgency.