Reopening of the NATO supply routes via Pakistan to Afghanistan would top the agenda of the meet, AAJ News reported.

The routes were blocked after a NATO air strike on a Pakistan Army border post killed 24 soldiers in November.

The planned talks were cancelled at the last-minute Saturday after the Pakistani leader's plane got delayed.

"This cancellation is due to a scheduling problem," said NATO spokeswoman Carmen Romero, on the eve of the two-day NATO summit in Chicago.

She said a bilateral meeting could still be held between the two before the summit ends Monday.

On Saturday, the NATO chief urged Islamabad to back efforts to stabilize Afghanistan.

Zardari was invited to the summit amid expectations that Pakistan will lift the six-month blockade against NATO supply trucks.

NATO has also asked Islamabad to do more to prevent insurgents from taking advantage of the porous Afghan-Pakistani border region to take sanctuary inside Pakistan.

"We can't solve the problems in Afghanistan without the positive engagement of Pakistan," Rasmussen said at a forum in Chicago.

US President Barack Obama is hosting the two-day summit that will focus on plans to hand over security to Afghan forces and withdrawal of foreign troops by 2014.

Pakistani Foreign Minister Hina Rabbani Khar and Foreign Secretary Jalil Abbass Jilani are accompanying Zardari.