By Jibran Ahmad PESHAWAR, Pakistan (Reuters) - Pakistan is to review its relationship with the United States, the prime minister's office said on Sunday, following the killing of the Pakistani Taliban leader in a U.S. drone strike. Mehsud, who had a $5 million U.S. bounty on his head, was killed on Friday in the northwestern Pakistani militant stronghold of North Waziristan, near the Afghan border. The Pakistani Taliban have killed thousands of Pakistani civilians and members of the security forces in their bid to impose Islamist rule, but the new government has been calling for peace talks. The government denounced Mehsud's killing as a U.S. bid to derail the talks and summoned the U.S. ambassador on Saturday to complain.