At least 21 people have been killed in drone strikes in Pakistan's North Waziristan days after the South Asian country agreed to reopen the NATO supply routes into Afghanistan.
According to official sources, six missiles were fired from a US drone at a compound in Gharlamay village of Datta Khel town near the border with neighbouring Afghanistan.
Security officials identified the dead as "militants".
It was the first drone attack since Islamabad reached a deal with Washington to reopen land routes into Afghanistan after the US apologised for the deaths of 24 Pakistani soldiers in an air strike in November last year.
The initial strike on a house killed nine. Then three others were killed in a second attack when they drove to the site to recover dead bodies. And a third drone killed another three five minutes later, a senior security official in Peshawar told the AFP news agency.
A similar attack in the region on Sunday killed six.
Akbar Ahmed, former Pakistan ambassador to the UK, said: "It can’t go against the will of the people and Pakistan is quite unanimous in rejecting the drone strikes on its territory."
"All the political parties, parliament and military have categorically condemned the strikes," he said.
Ahmed told Al Jazeera: "We know that in the past there were all kinds of backdoor dealings - we are told we don’t know for sure - between Pakistan and the US which sort of winked and nudged and looked the other way while drone strikes would be conducted."
"Now those days have gone because the relationship between the two country is so brittle and tense. And anything smacking of backdoor dealings would really risk a reaction in the public against the government in Pakistan," he said.
The US has stepped up drone attacks in North Waziristan in recent weeks in an area seen as a hub for armed groups who attack US forces and their allies in Afghanistan.
Datta Khel is considered a stronghold of Hafiz Gul Bahadur, a Taliban commander accused of sending fighters across the border to fight NATO troops in Afghanistan.
Many Pakistanis say drone attacks that kill civilians are a violation of Pakistani sovereignty.
Meanwhile, there have been protests in major Pakistani cities over the re-opening of supply routes. The Taliban has promised to attack NATO supply trucks traveling along Pakistani roads into Afghanistan.