Chicago/Islamabad, May 21 (IANS): US Special Representative for Afghanistan and Pakistan Marc Grossman has said that some differences exist with Pakistan and it will take time for the issues to be resolved, Dawn News reported Monday.

Talking to journalists after the meeting between Pakistani President Asif Ali Zardari and US Secretary of State Hillary Clinton, the US special envoy said that some difference remain between the two countries.

The meet took place amidst continued tensions over US air strikes last November that killed 24 Pakistani soldiers, leading to the closure of the supply routes.

Grossman said, however, the process of negotiations between the two countries continued and efforts were being made for the resolution of contentious issues.

He added that terrorism was a mutual problem which required to be jointly fought against.

As a NATO summit opened here amid protests, the US failed to strike a deal with Pakistan to reopen supply lines to Afghanistan, casting a long shadow over talks to end the alliance's combat role in the Afghan war.

US President Barack "Obama remained at loggerheads with President Asif Ali Zardari of Pakistan, refusing even to meet with him without an agreement on the supply routes," the New York Times reported.