At least four people were killed and five others injured in a U.S. drone attack launched Sunday in Pakistan's northwest tribal area of South Waziristan, according to local media reports.

At about noon time, a U.S. drone reportedly fired four missiles at a house in the area of Shaktoi in South Waziristan, a tribal area bordering Afghanistan, which is believed to be a stronghold of the Taliban militants.

The house targeted is believed to be one of the residences of the deceased Taliban leader Baitullah Mehsood who was reportedly killed in a U.S. drone strike in August 2009.

A vehicle parking near the house was also reportedly blown up by the missiles fired by the U.S. drone, said local sources.

Sunday's strike is the second of its kind in the past two days. On early Saturday morning, a U.S. drone fired five missiles at a suspected militant hideout in South Waziristan, killing at least 16 people and injuring many others.

Since August 2008, the U.S. air force launched an estimated 221 drone attacks in Pakistan's northwest tribal areas bordering Afghanistan, reportedly killing nearly 950 people while injuring hundreds of others.

The U.S. drone strikes are considered as a serious violation of Pakistan's territorial air space right and they are an important factor contributing to the anti-American sentiment prevailing across the country as most of the killed and injured in the drone attacks are reportedly innocent civilians.