At least seven people were killed as a second U.S. drone attack hit northwest Pakistan's North Waziristan tribal region Tuesday, local sources said.

Locals said two missiles were fired by the U.S. drone fighter jet at a vehicle near Miranshah, the main town in North Waziristan bordering Afghanistan. Several people were also injured.

Earlier on Tuesday, at least 14 people were killed in a U.S. drone strike on houses and a car in Datta Khel in North Waziristan, local sources said.

The identity of the dead were not immediately clear, nor was there any information on any high-value targets.

Tribesmen said spy planes were hovering over the region and making low flights before the attack.

U.S authorities claim drone attack target militants in Pakistan 's lawless tribal regions across the Afghan border.

Although Pakistan publicly opposes the attacks, saying they violate its sovereignty and fuel anti-American sentiment, it is believed that it was sharing intelligence with the U.S. about the insurgents and their hideouts.

More than 900 people have been killed in more than 90 U.S. drone strikes in Pakistan since August 2008, including at least 32 such attack so far this year.

The U.S. has stepped up strikes in North Waziristan after Taliban leader Hakimullah Mehsud appeared in a video with Hammam Khalil Al-Balawi, the Jordanian suicide bomber who killed seven CIA operatives in a forward base in Afghanistan's Khost province in December 2009.