ISLAMABAD - NATO has invited Pakistan President Asif Ali Zardari to the upcoming Chicago summit on Afghanistan, in what could be seen as a sign of Islamabad preparing to reopen its western border to the U.S. and NATO military supplies.

Pakistan had blocked the routes in November last year in protest after 24 of its troops on the Afghan border were killed in a US air attack.

Meanwhile, Pakistan has confirmed that Zardari will attend the May 20-21 NATO summit.

Nadeem Hotiana, a Pakistani embassy spokesman in Washington, said Tuesday that Zardari would be attending.

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

"This meeting will underline the strong commitment of the international community to the people of Afghanistan and to its future," NATO spokeswoman Oana Lungescu said in Brussels, where the alliance is based. "Pakistan has an important role to play in that future."

According to the President's office, this was an unconditional invitation and not linked to the reopening of the ground lines of communication (GLOC/ NATO supply lines) or any other issue.

The invite came ahead of a meeting in Pakistan of civilian and military leaders to discuss the blockade.

Pakistan Prime Minister Yusuf Raza Gilani's office said that ministers had backed a proposal to allow NATO to send only non-lethal equipment into Afghanistan on Pakistani roads.

"It was also decided that the military authorities should negotiate fresh border ground rules with NATO ... to ensure that incidents [such as November's air strike] do not reoccur," the statement said.

The cabinet is scheduled to meet on Wednesday to discuss the issue.