Islamabad: The US stepped up its drone campaign in Pakistan`s tribal belt after authorities in Islamabad failed to act on intelligence about the involvement of North Waziristan-based militants in coordinated attacks in Kabul on April 15, a media report said on Friday.
Upset over Pakistan`s alleged inaction against those groups and identified targets in intelligence provided by Washington, the US acted directly and began pounding the militants with drones, the Dawn newspaper quoted military and intelligence sources as saying.
The CIA carried out six drone strikes last month, against an average of three a month this year.
The pattern has continued with three drone attacks in the first week of June, one of which killed al Qaeda No 2 Abu Yahya Al-Libi in Mirali, a town in North Waziristan Agency.
The report said the US had provided specific intelligence related to the Kabul attacks, including sites where the improvised explosive devices were suspected to have been manufactured for use in the terrorist assault.
The IED factories pointed out by the US were in North Waziristan, it said.
The US presented evidence of the involvement of the Haqqani network and the Taliban as well as the "collusion of some of their Pakistani affiliates", the report said.
Due to the sensitivity of the issue, the sources did not tell the Dawn when and at what level the intelligence was shared with Pakistan.
Pakistan noted the concerns of the US but officials appeared hesitant in accepting that groups based in North Waziristan were involved in the attacks.
There was no "appreciable action by the Pakistani side" and "the US acted against some of those targets using drones", the report said.
An unnamed Army officer, who was aware of intelligence cooperation between Pakistan and the US, rejected the allegations made by Washington.
Pakistan has maintained that US drone strikes are illegal and a violation of its sovereignty and territorial integrity.
Parliament has demanded the end of drone strikes. US Charge d`Affaires Richard Hoagland was earlier this week summoned to the Foreign Office and a protest note on drone attacks was handed over to him.
The April 15 attacks in Kabul led to the hardening of the US stance on Pakistan.
The incident not only made the US administration to go back on its promise of apologising for a deadly cross-border NATO air strike last year, but also caused it to get tougher on Pakistan, particularly in negotiations on new terms of engagement.