Airstrikes and clashes in southern Afghanistan killed more than 75 militants, and NATO announced a new offensive against the Taliban in the world's largest opium-producing area, officials said Tuesday.

A threatened deadline for the lives of 23 South Korean hostages again passed with no resolution, as Korean negotiators met with the kidnappers and a purported Taliban spokesman said the talks were in the "final stage."

Afghan and U.S.-led coalition troops called in airstrikes after being ambushed by militants in southern Helmand province, the U.S.-led coalition said. The coalition said at least 36 insurgents were killed in the fighting Monday, but no Afghan or coalition troops were hurt.

In neighboring Uruzgan province, police clashed for three days with militants blocking the road leading to Kandahar province, leaving 26 militants and two policemen dead, said Wali Jan, the Uruzgan deputy highway police chief. NATO-led and Afghan army troops joined the battle Tuesday, reopening the road for civilian traffic, he said.

Another 13 suspected militants were killed in Kandahar province, the Defense Ministry said.

The battles took place in remote and dangerous parts of Afghanistan, and the death tolls could not be independently confirmed.

Violence has spiked sharply in Afghanistan the last two months. More than 3,500 people, mostly militants, have been killed in insurgency-related violence this year, according to an Associated Press tally of casualty figures provided by Western and Afghan officials.

NATO-led troops, meanwhile, announced a new offensive in the world's largest drug producing region — Helmand province. The mission aims to clear insurgents from Gereshk district to help foster economic projects.

In Ghazni province, Korean negotiators, accompanied by Afghan elders and clerics, met the kidnappers in person, said a provincial official who asked not to be identified because of the sensitivity of the situation.

The official also said the militants were now demanding monetary payment for the release of the hostages. Previously, Qari Yousef Ahmadi, the purported spokesman, said the militants wanted 23 Taliban prisoners released for the lives of the hostages.

Ahmadi late Tuesday said the negotiations were in the "final stage" but he provided no other details.

The South Korean Defense Ministry, meanwhile, said it asked the Afghan military to refrain from conducting operations near the hostages out of concern the kidnappers could be provoked.

Villagers in Ghazni held a rally demanding the hostages be released, said Mohammad Zaman, the deputy provincial police chief. Some carried banners and shouted slogans calling for the Koreans to be freed. An AP Television News reporter saw 100 to 150 villagers demonstrating.

The South Korean hostages, including 18 women, were kidnapped on Thursday while riding on a bus through Ghazni province on the Kabul-Kandahar highway, Afghanistan's main thoroughfare.

Ahmadi also said the militants are still holding one German and four Afghan hostages, despite Ahmadi's claims Saturday that those hostages had been shot and killed.