ISLAMABAD, Pakistan - NATO on Tuesday invited Pakistan's president to next week's Chicago summit on Afghanistan, the strongest sign yet that Islamabad is ready to reopen its western border to U.S. and NATO military supplies heading to the war in the neighboring country.

Pakistan blocked the routes in November after U.S. air strikes killed 24 of its troops on the Afghan border. The attack sent ties between Washington and Islamabad to new lows, threatening regional cooperation needed for negotiating an end to the Afghan war.

The developments signal something of a rapprochement, but tensions are likely to bedevil what has long been a brittle relationship, scarred by mistrust on both sides. Many in Washington believe Pakistan is supporting the Taliban, making the Afghan war unwinnable.

The United States expressed regret for the air strikes and has been quietly pressing Pakistan to reopen the routes over the last two weeks. Washington and NATO stepped up those efforts in recent days, and officials had said Islamabad would not be welcome at the two-day summit beginning Sunday in Chicago unless it did so.

NATO Secretary-General Anders Fogh Rasmussen phoned President Asif Ali Zardari on Tuesday afternoon to invite him to the meeting, according to a statement from the Pakistan government and NATO.

In Islamabad, Zardari spokesman Farhatullah Babar said the president would consider the invitation.

Pakistani civilian and military leaders later met to discuss the possibility of lifting the supply-line blockade. In a statement, the cabinet's defense committee endorsed the invitation to Chicago, suggesting that Zardari would accept it.