By Augustine Anthony

ISLAMABAD, PAKISTAN - Suspected U.S. drone aircraft fired missiles at militant targets in Pakistan's South Waziristan tribal region on the Afghan border on Thursday, killing at least five people, intelligence officials said.

The United States, alarmed by worsening security in Afghanistan, has been using pilotless drone aircraft to attack Taliban and al Qaeda fighters in northwestern Pakistani enclaves, from where the militants mount attacks into Afghanistan.

At the same time, nuclear-armed Pakistan is struggling to push back a growing Taliban insurgency of its own. Its security forces have been fighting the Islamist militants in the Swat valley, northwest of Islamabad, for more than a month.

At least two of the pilotless aircraft used in Thursday's strikes hit two separate areas in the Taliban and al Qaeda stronghold of South Waziristan, the intelligence officials said.

The Pakistan military has been softening up targets in the area and is expected to expand its Swat offensive against the Taliban into South Waziristan soon.

"Three missiles struck a training camp run by a local militant commander, Malang Wazir," said an intelligence official, who asked not to be identified, referring to an attack in a village west of the region's main town of Wana. Another security official, citing witnesses, said five people had been killed in the same strike.

The second attack was in a separate village but neither of the officials had any details about casualties there.

U.S. ally Pakistan objects to the U.S. missile strikes, saying they violate its sovereignty and undermine efforts to deal with militancy because they inflame public anger and bolster support for the militants.

Washington says the missile strikes are carried out under an agreement with Islamabad that allows Pakistani leaders to publicly criticise the attacks. Pakistan denies any such agreement.

(Editing by Paul Tait)