KABUL: The Pakistan-based Haqqani network was responsible for a series of attacks in Afghanistan this week, the US ambassador to Kabul said Thursday, and Islamabad is being pressed hard to take action against them.

The attacks on Sunday, including the biggest assault on the capital in 10 years of war, saw squads of militants fire on government offices, embassies and foreign bases.

"There is no question in our mind that the Haqqanis were responsible for these attacks," ambassador Ryan Crocker told reporters in Kabul.

"We know where their leadership lives and we know where these plans are made. They're not made in Afghanistan. They're made in Miranshah, which is in North Waziristan, which is in Pakistan," Crocker said.

"We are pressing the Pakistanis very hard on this. They really need to take action."

Islamabad denies any support for Haqqani activities, but former US military chief Admiral Mike Mullen described the network a "veritable arm" of the Pakistan Inter-Services Intelligence agency.

Closely affiliated with the Taliban, the group was founded by Jalaluddin Haqqani during the war against the Soviet occupation of Afghanistan in the 1980s, when it received covert US aid.

Apart from Kabul, the eastern capitals of Paktia, Logar and Nangarhar provinces also came under attack Sunday, with a total of 51 people, including 36 militants, killed.

In September last year, US officials accused the network of a similar attack on the US Embassy in Kabul as well as a truck bombing on a NATO outpost in the same month that injured more than 70 US soldiers.

Washington and Islamabad are in the process of trying to rebuild their fractious relations, in crisis after last year's discovery of Osama bin Laden in Pakistan and a US air raid that mistakenly killed 24 Pakistani soldiers. (AFP)