Secretary General Anders Fosh Rasmussen on Thursday expressed deepening unease at a growing disparity in defense spending between the United States and European allies due to economic pressures on eurozone governments.

"Defense spending among the allies is increasingly uneven, not just between North America and Europe, but also among European allies," Rasmussen said in an annual address in Brussels.

The first of six batteries of Patriot missiles deployed in Turkey to protect against a spillover of the conflict in neighboring Syria became operational on Saturday, NATO said.

The battery, provided by The Netherlands, "will help to protect the (southern) city and people of Adana against missile threats," it said in a statement.

Hillary Clinton Wednesday bade farewell to her NATO allies after making her last appearance as U.S. Secretary of State here, praising the military alliance for having made "great strides".

"I've spent a bit of my time in this building over the past four years, and I think it was time well spent," Clinton mused, speaking after two days of talks among the 28-member alliance in Brussels.

Afghan and NATO forces foiled a series of suicide attacks on Kabul planned for Sunday when they captured five insurgents allegedly linked to militants in Pakistan, officials said.

The group was "finalizing plans for an attack in the capital" and a large cache of explosives, suicide vest parts, weapons and ammunition were seized in the overnight operation, NATO's International Security Assistance Force said.

Insurgent attacks in Afghanistan rose by 11 percent in the past three months over the same period last year, according to the latest figures released by NATO's U.S.-led coalition.

The month of June alone accounted for the highest number of attacks in nearly two years, with more than 3,000 assaults, including firefights and the explosion of homemade bombs, the International Security Assistance Force said.

Three soldiers from the U.S.-led NATO mission in Afghanistan and an Afghan interpreter were among those killed in an attack on a military patrol Wednesday, officials said.

The U.S. embassy in Kabul released a statement confirming that three members of the International Security Assistance Force and the interpreter were killed. An ISAF official told AFP the three personnel were soldiers.

The U.S. commander of NATO forces in Afghanistan has apologized over the deaths of civilians in an air strike this week, flying personally to the scene to deliver his condolences.

President Hamid Karzai had expressed outrage over the incident in which Afghan officials said 18 civilians including women and children were killed, and cut short a visit to Beijing to return home.

NATO has no intention of intervening in Iran and backs a diplomatic solution to the nuclear dispute, the alliance's chief said Thursday, after reports of a debate in Israel over launching an attack.

"Let me stress that NATO has no intention whatsoever to intervene in Iran and NATO is not engaged as an alliance in the Iran question," Secretary General Anders Fogh Rasmussen said at a news conference.

An Afghan provincial governor Sunday said 18 civilians and 20 police were killed by "friendly fire" during U.S.-led air strikes against insurgents in the northeast of the country.

The governor of Nuristan, which was the scene of heavy battles last week between the Taliban and Afghan security forces, said the police and civilians were targeted Wednesday after they were mistaken for militants.