UNITED NATIONS, (Reuters) – The head of NATO expressed concern on Thursday about armed groups operating outside government control in Libya and said he was encouraging Tripoli to accept an offer of help to reform its security sector.

NATO Secretary-General Anders Fogh Rasmussen made the offer to Libyan leader Mohammed Magarief after this month’s attack on the U.S. consulate in the eastern Libyan city of Benghazi, which killed the U.S. ambassador and three other Americans.

“Obviously, it is a matter of concern that individual and independent armed groups operate without superior control in Libya,” Rasmussen told Reuters in an interview on the sidelines of the United Nations General Assembly in New York.

He said he had offered NATO help to improve security in Libya in a meeting with Magarief at the United Nations.

“We have a lot of expertise when it comes to reforms of the defense and security sector and also when it comes to the reintegration of former freedom fighters to a unified security structure in the new Libya,” he said.

“If the new Libya authorities so wish, NATO stands ready to help them in reforming their defense and security sector. We take that very seriously.”

Rasmussen said he was encouraged that the new Libyan government had taken “a number of steps to put these individual groups under control with the aim of creating a strong unified security structure.”

NATO mounted a seven-month campaign of air strikes on Libya last year that helped bring about the overthrow of Muammar Gaddafi by rebel groups. It first made the offer to support security reform last year, but Libya has not yet accepted.

In New York on Monday, Magarief personally apologized to U.S. Secretary of State Hillary Clinton for the consulate incident, which Washington says was a terrorist attack.

Magarief has said that some of those arrested for involvement in the attack were not Libyans and were linked to al Qaeda, the radical Islamist organization responsible for the Sept. 11 attacks on the United States in 2001.

Libya’s government has sought to impose order on armed groups and the military has said it has removed the heads of two of the most powerful militias operating in Benghazi..

U.S. WITHDRAWS TRIPOLI EMBASSY STAFF

Underscoring continued security worries, the United States said on Thursday it was temporarily withdrawing more staff from its embassy in Libya’s capital Tripoli, but hoped they could return early next week.

Rasmussen reiterated that NATO had no intention to intervene in Syria as it had in Libya, but stood ready to defend NATO member and Syria’s neighbor Turkey, should this be necessary.

“We do believe that the way forward in Syria is a political solution,” he said. “Syria is a very complex society, religiously, ethnically, politically. Any foreign intervention may have unpredictable repercussions.”

Rasmussen said an Oct. 9-10 meeting of NATO defense ministers in Brussels would discuss a decision to halt joint operations by NATO-led foreign troops and Afghan forces in Afghanistan after a spate of killings of NATO soldiers by Afghans they were training.

He stressed that the measure was “temporary,” but could not say when it might be lifted. “That decision will be taken on the ground based on a complete evaluation of the security situation.”

The U.S. Department of Defense said on Thursday that NATO-led forces were resuming operations alongside their Afghan counterparts in growing numbers, a week after commanders curtailed some joint missions due to a surge in insider attacks and tensions over an anti-Islamic video.

The Pentagon did not provide precise figures on the extent of the increase in partnering since the new policy was enacted. But U.S. Defense Secretary Leon Panetta said in Washington that most units in Afghanistan were conducting “normal partnered operations at all levels.”

Rasmussen said joint operations remained an important element in training Afghan forces to ensure they can take complete responsibility for security and allow foreign troops to end their combat role by the end of 2014 as planned.

He said the “insider attacks” were a matter of great concern as “they threaten to undermine trust and confidence between international troops and Afghan security forces,” but added:

“They do not define the overall relationship between international troops and Afghan security forces and they definitely will not derail our strategy.”

Rasmussen said the Brussels meeting would discuss the first steps in planning the training mission NATO will lead in Afghanistan after 2014.

“We have not yet decided how many trainers we will need – we are examining that,” he said. “At the end of the day, it will very much depend on the concrete security situation and the capacity of the Afghan security forces by the end of 2014.”

Rasmussen said NATO’s planning assumption was that the cost of maintaining Afghan security forces after 2014 would be around $4 billion annually, of which non-U.S. members of NATO and partner countries would contribute $1.3 billion a year.

“We are not there yet,” he said when asked how much had been pledged for this purpose, “but we have received announcements of quite substantial financial contributions already.”