Suspected Taliban (search) militants raided a village and killed nine tribesmen, and vengeance-seeking relatives killed four people in another hamlet, an official said Thursday, as violence simmered ahead of key parliamentary elections.

Elsewhere, American forces killed a militant and wounded another Wednesday after coming under attack in Zabul (search) province, which borders Pakistan, a U.S. military statement said.

Militants linked to the Taliban, which was toppled by U.S.-led forces in 2001, have stepped up attacks in recent weeks in an apparent effort to disrupt Sept. 18 parliamentary elections. More than 700 people have died in a surge of attacks since March.

But the commander of Afghanistan's International Security Assistance Force (search) — a NATO-led force of 8,000 troops responsible for protecting Kabul and much of the country's north and west — said security would be tight for the poll.

"I'm sure there will be no problem," Lt. Gen. Ethem Erdagi said at a news conference.

NATO plans to boost ISAF by 3,000 troops, who will provide security for thousands of candidates and hundreds of polling stations. NATO similarly boosted its peacekeeping force during the presidential elections last October.

On Sunday, a female Afghan election worker was shot and wounded about two miles from a voter registration station in northeastern Nuristan province, officials said Thursday.

The nine ethnic Hazaras were killed when rebels raided their village Monday in central Uruzgan province, Gov. Jan Mohammed Khan said. The victim's relatives staged a retaliatory raid Wednesday against a nearby ethnic Pashtun hamlet, killing four people, he said.

The Taliban are mostly of Pashtuns, the dominant ethnic group in southern Afghanistan.

Security forces were deployed to the region to reduce tension between the two communities, Khan said.

Also Wednesday in the country's main western city of Herat, two small bombs exploded but caused no casualties or damage, in an attack thought to be linked to a local power struggle.

The blasts occurred outside the police chief's office and on a roadside near the governor's residence, said provincial Gov. Sayed Hussain Anwari.

The bombs were thought to have been laid by local people embroiled in a political struggle, Anwari said. No suspects have been arrested, but an investigation is underway, he said.

On Tuesday, a suspected suicide bomber died in a failed assassination attempt against a district chief in the region.

Herat has been spared much of the violence that has wracked Afghanistan's southern and eastern provinces since March.