ISLAMABAD (AP) — An unmanned American aircraft fired missiles at a vehicle in a Pakistani tribal area bordering Afghanistan Tuesday, killing five suspected militants and injuring two, Pakistani intelligence officials said.

The strike was part of a spike in American drone attacks, which have drawn official Pakistani criticism in the past. The spurt of drone action threatened to add tensions to relations between the two allies, just as they appeared to be improving.

The latest drone strike came near Shana Khora village in North Waziristan, two officials said.

They said the area of the drone attacks is dominated by anti-U.S. militant commander Hafiz Gul Bahadur. The officials spoke on condition of anonymity because they were not authorized to brief reporters.

Bahadur's group is known for frequent attacks on U.S. troops in Afghanistan, but generally it does not carry out operations inside Pakistan. Several recent drone strikes have killed militants affiliated with Bahadur's group.

Tuesday's was the third drone attack in North Waziristan within three days. On Sunday, drone-fired missiles killed 10 suspected militants in two strikes 12 hours apart.

The covert CIA drone program has drawn strong criticism in Pakistan. Pakistani officials charge such strikes violate their country's sovereignty. Many Pakistanis complain that the strikes kill innocent civilians.

The U.S. insists that drone strikes are essential to combat militant groups, like al-Qaida. There is evidence that despite their critical public stance, the Pakistanis have sometimes quietly condoned the drone attacks.

The U.S. complains that the Pakistani army has carried out offensive against militants in all other tribal regions, but not North Waziristan. The area has become a safe haven for militants, who use it as a base to attack American and other NATO troops in neighboring Afghanistan.

Pakistan has resisted U.S. pressure for action in North Waziristan, saying its military is already overtaxed by fighting in other parts of the country. Analysts have said Pakistan does not want to engage militant groups that could be allies in Afghanistan after foreign forces leave. NATO is due to hand over security responsibility to Afghan forces at the end of 2014.

Relations hit a snag after American airstrikes killed 24 Pakistani soldiers in November. Pakistan closed down the main NATO supply route to Afghanistan in response. The route was re-opened only seven months later, in July, after the U.S. apologized, and ties began to improve.

Also Tuesday, a roadside bomb targeting a security convoy killed at least one civilian and wounded eight others in southwestern Pakistan.

Senior police officer Abdul Majid Bhatti said no soldiers were hurt in the attack on the outskirts of Quetta, the capital of Baluchistan province.

No group claimed responsibility, but suspicion fell on nationalists who have waged an insurgency in Baluchistan for decades, demanding autonomy and a larger share of the province's natural resources. They often target Pakistani security forces.