KABUL, Afghanistan - "Clear evidence" exists that some Taliban fighters have trained in Iran, the commander of NATO and U.S. forces in Afghanistan said.

Gen. Stanley McChrystal told reporters Sunday in the Afghan capital that Iran -- Afghanistan's western neighbour -- has generally assisted the Afghan government in fighting the insurgent group.

"There is, however, clear evidence of Iranian activity -- in some cases providing weaponry and training to the Taliban -- that is inappropriate," he said. McChrystal said NATO forces are working to stop both the training and the weapons trafficking.

Last month, McChrystal said there were indications that Taliban were training in Iran, but not many and not in a way that it appeared it was part of an Iranian government policy. He did not give details on how many people have trained in Iran at Sunday's news conference.

The U.S. command confirmed that an American service member was killed Sunday in a small arms attack in southern Afghanistan. May is already the deadliest month this year for U.S. troops with 33 deaths -- two more than in February when American, NATO and Afghan forces seized the Taliban stronghold of Marjah in Helmand province.

The month also brought the 1,000th U.S. military death in the Afghan war since it began in 2001 when Marine Cpl. Jacob Leicht was killed Thursday by a roadside bomb in Helmand.

The AP's figures are based on Defence Department reports of deaths as a direct result of the Afghan conflict, including personnel assigned to units in Afghanistan, Pakistan or Uzbekistan. Non-U.S. deaths are based on statements by governments that have contributed forces to the coalition.

The Taliban have spread out beyond their heartland in the south in recent years to increasingly launch attacks countrywide.

In the north, insurgents detonated a remote-controlled bomb Sunday as a police convoy passed by, killing seven officers in a province previously considered to be relatively safe, said deputy provincial Gov. Shams-ul Rahman.

The attack was the deadliest of a half-dozen separate incidents across the country.

In nearby Kunduz province, militants attacked a police checkpoint in Ali Abad district, triggering a gunbattle that killed three insurgents and wounded seven others, the Interior Ministry said.

Eight Afghan police were wounded Sunday by a suicide bomber who struck a checkpoint on the outskirts of Khost City southeast of Kabul, officials said.

And NATO and Afghan forces killed one suspected militant and detained several others at a compound in Helmand where bomb-making equipment was found. Coalition patrols arrested other suspected insurgents in operations elsewhere in Helmand and neighbouring Kandahar, both considered Taliban strongholds.

Also Sunday, Canada said the chief of its forces in Afghanistan, Brig. Gen. Daniel Menard, was being relieved following allegations of an inappropriate relationship. Col. Simon Hetherington, the acting commander of Canada's forces, said Menard's dismissal would not have an impact on the Canadian mission in southern Afghanistan.