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."