ISLAMABAD (AP) — American attempts to rebuild its relationship with Pakistan appear to be stuck on the issue of a U.S. apology for killing 24 Pakistani border troops last November.

U.S. officials visited Pakistan on Friday for talks on rebooting the relationship, but left without any agreement. A statement Saturday from the Pakistani president's office said Asif Ali Zardari told the visiting U.S. officials that Washington needed to help Pakistan reach "closure" over the killings of the soldiers on the Afghan border by following recommendations by the Pakistani parliament.

The parliament has asked Washington to apologize for the incident. The United States has expressed regret, but has declined to specifically say it is sorry.

Pakistan shut U.S. and NATO supply lines to Afghanistan to protest the deadly U.S. air strikes, cut most contacts with Washington and ordered American drone aircraft to leave a base in the south of the country. The U.S. wants Pakistan to reopen the supply lines, preferably ahead of a May 20-21 summit of NATO leaders in Chicago.

The Defense Department has said U.S. forces — given what information they had available to them at the time — reacted in self-defense and with appropriate force after being fired upon from the direction of the Pakistani border in the Nov. 26 incident.

The visit by Mark Grossman, who is Washington's envoy for Afghanistan and Pakistan, was his first to Pakistan since the November incident.

Pakistan used the border incident to try to extract better terms from Washington, which sees Pakistan as an essential — if unreliable — ally against al-Qaida and vital to the sustainability of any peace deal with insurgents fighting in neighboring Afghanistan.

The border deaths were the latest in a series of incidents over the last 18 months that severely damaged U.S.-Pakistani relations. The killing of two alleged Pakistani assailants by CIA security officer Ray Davis in Lahore in January 2011 and the U.S. Navy SEAL raid that killed Osama bin Laden in Pakistan in May, without Pakistani permission, also contributed to the decline.