KABUL (AFP/Reuters) - The Pakistani-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.”

Pakistan denies that claim.

“Thousands of Pakistanis have died in terrorist actions inside Pakistan from individuals and groups that are in these so-called safe haven areas,” said Crocker. “So they really need to take action and that is going to be a major part of our dialogue going forward. That’s what we are pressing them to do.”

The US assertion that the Haqqanis were behind the recent attacks on Kabul and elsewhere, and renewed calls for Pakistani action against the group, could deepen strains in the strategic alliance between Washington and Islamabad.

A Pakistani intelligence official expressed concern that the American assertion would bring renewed pressure on Pakistan to launch a major operation in North Waziristan.

“What we are worried about is the pressure that’s going to come over North Waziristan,” he told Reuters. “We have no connection to the attack.”

Crocker said the insurgent death toll during the weekend attacks suggested the Haqqanis were not gaining strength.

The operations, however, may have been designed to make big headlines, not inflict big casualties.

“They clearly have an ability to launch attacks against multiple targets, but the effectiveness of these attacks in highly limited,” said Crocker.

“That doesn’t mean we should brush them off.”

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.