Pakistani intelligence officials say a U.S. drone strike has killed at least four suspected militants in the country's northwest, along the Afghan border.

The missiles fired from a pilotless aircraft hit a vehicle near Wana, the main town in the South Waziristan tribal region. The area is a known stronghold of Taliban and al-Qaida-linked insurgents.

Monday's drone strike was the first reported in Pakistan's tribal region since July 12.

U.S. officials have never publicly acknowledged the use of such strikes inside Pakistan but privately have confirmed their existence to various news outlets. Pakistan has condemned the attacks as a violation of its sovereignty, but the drone strikes are believed to be carried out with the help of Pakistani intelligence.

Elsewhere in Pakistan, police say gunmen set fire to seven tankers carrying fuel to NATO forces in neighboring Afghanistan. Monday's attack took place in the Khairpur district of Sindh province. At least one person was injured in the attack.

Meanwhile, the Human Rights Commission of Pakistan said Monday that the ongoing deadly violence in Sindh's capital, Karachi, is largely a result of dissension between the city's main political groups.

Police say at least 12 people have been killed in various attacks in Karachi since Sunday, with more than 200 people dead from political and ethnic violence in Pakistan's economic hub in July.

Authorities say the killings are part of clashes between the MQM, which largely represents the Urdu-speaking community, and its rival, the Awami National Party , which represent ethnic Pashtuns. Both those parties and the ruling Pakistan People's Party are believed to have links to armed groups in Karachi.

The commission concluded a three-day fact-finding mission to Karachi on Sunday.