PESHAWAR, Pakistan (Reuters) - U.S. drone aircraft fired four missiles in Pakistan's South Waziristan tribal region on Wednesday, killing six militants, days after the head of the country's intelligence agency called for an end to the strikes that have caused deep anger.

The missiles were fired from two unmanned planes and aimed at a vehicle in Baghar village 12 km (about 8 miles) east of the Afghan border, residents and officials said.

"I heard four blasts while several drone (aircraft) were flying over the area," Rahimullah Wazir, a resident, told Reuters.

A security official in the region said the missiles hit a vehicle carrying militants. "We have confirmation of six but toll could be high," he said.

The strike came two days after Lieutenant-General Ahmad Shuja Pasha, head of Pakistan's Inter-Services Intelligence, sought an end to the drone campaign during a meeting in the United States with CIA Director Leon Panetta, officials said.

The United States has been using drone attacks to target al Qaeda-linked militants over the past few years in Pakistan's lawless tribal areas, a source of concern for the Pakistan government because civilians casualties inflame public anger, and bolster support for militancy.