Seven deminers kidnapped in western Afghanistan have been beheaded by their abductors, police said Sunday, as NATO announced the deaths of three soldiers in Taliban attacks.

The seven were part of a group of 28 deminers who were snatched on Wednesday in a district that is the focus of the Taliban insurgency in Farah province, but no one has claimed responsibility for the mass kidnapping.

"Seven of the deminers are beheaded. We have recovered the body of one of them and the rest of the bodies are with tribal elders," said Mohammad Ghaws Malyar, the Farah provincial deputy police chief.

He said the fate of the other deminers who were taken in the Bala Buluk district was unknown.

Criminal groups and insurgents have repeatedly kidnapped dozens of Afghans and foreigners since a 2001 US-led invasion ousted the Taliban regime, but most are eventually freed for ransom or in exchange for the release of prisoners.

The deminers were working for the Demining Agency for Afghanistan, an Afghan charity based in the southern province of Kandahar.

In a similar incident in December, 18 Afghans working for the Mine Detection Center were kidnapped in the eastern province of Khost, which borders Pakistan, and were freed unharmed a day later in a joint Afghan-foreign operation.

Also Sunday, three NATO soldiers and three policemen were killed in bomb and insurgent attacks in the restive south and east, as the top US commander in the country said the overall number of insurgent attacks had decreased this summer.

NATO said one coalition soldier died following an insurgent attack and another was killed in a bomb explosion in the south, while a third service member died after another insurgent attack in the east.

In southern Kandahar city, three Afghan policemen were killed, while three policemen and three civilians were wounded, in a roadside bomb blast that ripped through a police vehicle, provincial police chief Abdul Raziqtold AFP.

Sunday's incidents brought the overall death toll for foreign forces to 293 this year in Afghanistan, according to a tally based on that collated by the independent website

Overall, however, General David Petraeus said attacks were down by "a few percent" for May and June, the beginning of the traditional annual fighting season, although he said the number of homemade bomb explosions had risen.

"June saw fewer insurgent attacks than last June and that's quite significant and May was quite the same," he said.

"So you have the first two months of comparison with the previous year is actually a reduction. July is trending that way. That is very significant," he told reporters in the Afghan capital Kabul.

Intelligence analysts had predicted a rise in insurgent attacks of 18 to 30 percent on last year, Petraeus said, while he cautioned that it was too early to declare the insurgency had been significantly hit.

Petraeus made his comments as he prepares to leave his post this month and as US and other coalition forces prepare to begin a gradual drawdown of combat troops, with all due to go home by the end of 2014.

US President Barack Obama has announced the withdrawal of the first 10,000 of nearly 100,000 US forces from Afghanistan this year, with another 23,000 to leave by the end of next summer.