The pact between the United States and Afghanistan could leave the door open for continued drone strikes against insurgent targets in Pakistan after 2014, US Ambassador Ryan Crocker indicated Wednesday.

"There is nothing in this agreement that precludes the right of self-defence for either party and if there are attacks from the territory of any state aimed at us we have the inherent right of self defence and will employ it," he said.

Crocker was responding to a question about controversial drone strikes on Taliban and Al-Qaeda targets in Pakistan at a briefing on the deal signed in Kabul overnight by US President Barack Obama and Afghan leader Hamid Karzai.

The Strategic Partnership Agreement states that the United States will not use its presence in Afghanistan to launch offensive actions against other states from Afghan soil.

However, it does say that in the event of threats to Afghanistan the two countries would consult on an appropriate response.

"This is defensive in nature, not offensive, doesn't threaten any one, but I hope the region takes notice," Crocker said.

US officials are loath to discuss the secretive CIA program, the source of sharp tensions between Washington and Islamabad. Drones have killed scores of what the US government says are Al-Qaeda suspects in Afghanistan, Pakistan and Yemen.

This week, Obama aide John Brennan insisted that the missile strikes were legal, ethical, proportional and saved US lives.

On Tuesday, the Pentagon warned that insurgent sanctuaries in Pakistan and corruption posed "long-term and acute challenges" to security in Afghanistan.

Crocker urged Pakistan to take action against safe havens and prevent cross-border attacks by the Taliban.

"I hope Pakistanis will take a look at this agreement and say 'Wow, the Americans are not going to cut and run this time. We don't need to hedge our bets, we don't need to put up with these guys any longer' and either take control of them or press them into the reconciliation process."