The United States is looking for evidence that the Pakistani spy agency, the ISI, played a role in Tuesday's attacks on the US Embassy in Kabul.

Given the ISI's history of supporting and sheltering members of the Haqqani network, it was "almost reflexive" to see if the spy agency had any a hand in the assault, a senior US defence official said.

"The possibility of ISI involvement was already being considered within hours of the attack's conclusion when President Barack Obama's National Security Council met Wednesday," the official said.

US defence secretary Leon Panetta has warned Pakistan that the US will take stronger action against it if the group isn't reigned in.

Evidence taken from the building from where the insurgents launched their rockets at the embassy showed that the insurgents were in touch with people outside Afghanistan, interior minister Bismellah Mohammadi said on Thursday.

"We found six mobile phones and all the evidence shows that the plot was sketched outside Afghanistan," General Mohammadi said in a video statement sent to the media.

Afghan and US officials have blamed the ISI for previous attacks, including the bombings of the Indian Embassy in Kabul in 2008 and 2009.