The United States said Thursday that Pakistan has let back in two officers to work with its military after a six-month gap, in what it called a small sign of cooperation after soaring tensions.

The Pentagon said that two liaison officers returned in the past week to the northwestern city of Peshawar after being kicked out by Pakistan in its outrage over a border airstrike that killed 24 of its soldiers.

But the Pentagon said that Pakistan has not let back trainers or reopened its border to NATO supplies, two of the main forms of support for the US-led war effort that have been shut down since the November 26 border incident.

The returning officers are in charge of liaising with the headquarters of Pakistan's 11th Corps, which covers the lawless border region where the US-backed ISAF force believes Al-Qaeda and Taliban fighters enjoy a safe haven.

"The tactical and operational coordination between the ISAF and Pakistani military is getting better -- in fits and starts, to be sure, but it is getting better," said Pentagon spokesman Captain John Kirby.

"This is another example of how that coordination is going to continue to improve," Kirby told reporters.

Kirby said that the two officers -- who report to the Bagram Air Base in Afghanistan -- returned to Peshawar at the request of Pakistan.

Relations between the United States and Pakistan have severely deteriorated in the past year, particularly after US forces discovered and killed Osama bin Laden in the country's military town of Abbottabad in May 2011.

Pakistan has demanded an apology over the November border killings. President Barack Obama has voiced regret, calling the deaths an accident, but stopped short of an apology amid US concerns that Pakistani intelligence elements are supporting extremists.

The NATO alliance invited Pakistani President Asif Ali Zardari to Chicago for a May 20-21 summit on Afghanistan's future. But the trip ended in debacle, with Obama snubbing Zardari after talks collapsed on reopening the border to NATO.

US lawmakers have since moved to cut aid to Pakistan -- which was totaled more than $18 billion since the September 11, 2001 attacks -- after a court gave a 33-year prison term to a doctor recruited by the CIA to find bin Laden.

Amid the tensions, the United States has stepped up its covert drone attacks inside Pakistan aimed at extremists deep in the tribal region. Pakistani officials said that two strikes on Monday alone killed at least nine militants.

Pakistan's parliament has demanded an end to drone attacks, saying they violate sovereignty and infuriate civilians. But the strikes enjoy wide support in Washington as they cause no US casualties and are seen as the only way to reach most-wanted militants.

However, at least 10 liberal lawmakers from Obama's Democratic Party have signed a letter to the White House voicing concern about what they see as a lack of oversight and accountability over the drone strikes.

Drones "are faceless ambassadors that cause civilian deaths and are frequently the only direct contact with Americans that the targeted communities have. They can generate powerful and enduring anti-American sentiment," said the letter spearheaded by Representatives Dennis Kucinich and John Conyers.