KABUL: US Defense Secretary Leon Panetta arrived in Afghanistan Tuesday to meet with commanders, as the US grapples with an eroding relationship with Pakistan that has complicated supply routes and helped fuel insurgents in the east.

While he was upbeat about security progress in Afghanistan, Panetta was also likely to hear some somber news from commanders as they wrestle with the withdrawal of 23,000 more troops in the coming year, the transition of security to Afghan forces and the near collapse of coordination with Islamabad along critical portions of the border.

His visit here is the second stop on a holiday tour that began in Africa and will also take him to Iraq, Libya and Turkey. He will be the first US defense chief to visit Libya, which is emerging from an eight-month civil war. In Iraq, he will participate in a ceremony that will shut down the US military mission there after nearly nine years of war.

Panetta's arrival in Kabul comes on the heels of Pakistan's decision to move air defense systems to the border with Afghanistan, part of its response to the Nato airstrikes last month that killed two dozen Pakistani forces. Pakistan has also closed two border crossings that are part of key supply routes into Afghanistan and recalled its troops from two border coordination posts.

The supply routes carry roughly 30 per cent of the fuel, food and other items needed for troops in Afghanistan. While Panetta said US troops in Afghanistan will get the supplies they need, the plummeting relationship with Pakistan complicates an already difficult war just as the Obama administration is trying to boast of security gains across broad swaths of the country.

''I think 2011 will make a turning point with regards to the effort in Afghanistan,'' Panetta told reporters traveling with him to Kabul. He cited lower levels of violence and the successful turnover of portions of the country to Afghan control. ''Clearly I think Afghanistan is on a much better track in terms of our ability to eventually transition to an Afghanistan that can govern and secure itself.''

Panetta said he has been reassured by Marine Gen. John Allen, the top overall commander of US and Nato forces in Afghanistan, that military operations are continuing along the Afghanistan-Pakistan border. He said Allen has reached out to Pakistani commanders to try to rebuild relations and cross-border communications that are vital in the rugged, mountainous region.

''I think it's been said a number of times,'' said Panetta. ''Ultimately we can't win the war in Afghanistan without being able to win in our relationship with Pakistan as well.''

Panetta was also likely to hear more about Allen's plans to take forces from the south, where the US hopes Afghan forces can cling to security gains made in the past year, and send them to the east to try and reverse gains by insurgents who have been launching high-profile attacks in Kabul.

Allen was ordered by Obama last summer to pull out 10,000 US forces by the end of this year and 23,000 more by the end of September 2012. There have been some rumblings that the administration may want to accelerate that drawdown, with an eye toward handing more control to the Afghans and shifting US troops into more of an advise-and-assist role.

The battlefield decisions are also complicated by the budget showdown in Washington. The Pentagon could face as much as $1 trillion in cuts over the next 10 years if lawmakers can't come to an agreement on the budget.

For Allen, however, the most immediate challenge will be getting fuel and other supplies to the troops now that Pakistan has closed two Afghan crossings in Chaman and Torkham, in the northwest Khyber tribal area. Bringing supplies in across the northern routes is more costly and time-consuming, but officials have not said how much more money it may cost, particularly if the Pakistan crossings are closed for months.

During previous cross-border incidents, Pakistan has closed border crossings for about a week or two. This time, however, US officials are worried the closings could drag on for months.

Right now, said Panetta, the troops have the supplies they need, and he said he is confident that as the US continues to work with Pakistan, the other routes will be restored.

On his historic Libya trip, Panetta said the US wants to help Libyans move in the right direction as the people take back their country. With military assistance from the US and Nato, Libyans ousted and later killed longtime leader Moammar Gadhafi earlier this year.

Panetta's plan to visit Libya comes amid ongoing violence there, including recent clashes between revolutionary fighters and national army troops near Tripoli's airport.