In the bloodiest fighting this year, U.S. Marines killed more than 80 insurgents in a three-week offensive against a Taliban (search) stronghold in the mountains of southern Afghanistan, the military said Saturday.

The U.S. military insisted the battle was a victory that will help secure fall elections — rather than a sign of the resilience of Taliban-led militants.

Two Marines were wounded in the fighting, the military said.

"The Marines have been aggressive, relentless and successful," U.S. military spokesman Lt. Col. Tucker Mansager said. "They have demonstrated that there is no refuge for the terrorists."

Some 2,000 Marines were sent to Afghanistan this spring, swelling the U.S.-dominated force to 20,000 — its largest yet — in an attempt to put rebels on the defensive ahead of September elections.

Militants have stepped up their own operations, feeding a spiral of violence that has left more than 450 people dead across the country this year.

Troops elsewhere had come under rocket and mortar fire several times in recent days but suffered no casualties, Mansager said.

In another operation, U.S. troops on Friday detained an expert bombmaker about 40 miles south of Kabul, Mansager said. He described the suspect as a "medium-value target" but declined to give more details.

The U.S. military and international peacekeepers based in Kabul have warned since last year that militants are increasingly using the kind of roadside bombs that have proved so deadly in Iraq.

Seven U.S. serviceman have been killed in southern Afghanistan (search) since early May — including four when a mine ripped through their Humvee — and dozens of Afghan soldiers have died in the region this year.

The Marines are based in Uruzgan Province, the home of fugitive Taliban leader Mullah Omar (search), and have called in warplanes to pound a large group of militants in nearby mountains.

Most of the fighting has been near Daychopan (search), in neighboring Zabul province, a rerun of clashes last summer that left more than 100 militants and one American special operations soldier dead.

Mansager said the Marines' offensive was allowing regular Army troops to focus on building ties with local communities across the troubled border region.

Commanders hope this approach, which includes millions of dollars in reconstruction aid, will persuade villagers and tribes to turn against the militants and provide intelligence.

It also is supposed to help safeguard the elections.

The United Nations has registered nearly one-third of the estimated 10 million voters but has yet to send voter registration teams into the most hostile areas.

Eleven rockets were fired at a convoy of U.N., government and American military officials in a lawless region near the Pakistani border on Friday, injuring no one.