NATO on Tuesday invited Pakistan's president to the upcoming 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 American airstrikes 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 between the two countries, 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 U.S. expressed regret for the airstrikes and has been quietly pressing Pakistan to reopen the routes over the last two weeks.