By Sharafuddin Sharafyar

HERAT, Afghanistan, Nov 6 (Reuters) - U.S.-led troops have killed at least seven civilians in an air strike in northwestern Afghanistan, officials said on Thursday, a day after the president said warplanes had killed 40 civilians in the south.

President Hamid Karzai said the issue of civilian casualties was the biggest source of tension with his main backers, the United States, and called on President-elect Barack Obama to make it his top priority to stop the killings of innocents.

The air strike was called in after a joint convoy of Afghan and U.S. forces came under an attack by Taliban insurgents in Ghormach district of Badghis province in the northwest late on Wednesday, provincial officials said.

District chief Abdullah said seven civilians and 15 insurgents were killed in the raid, but the head of the provincial council Qari Dawlat, quoting villagers, put civilian deaths at around 30.

A spokesman for the U.S. military said he was not aware of the report and would check the incident.

It was not possible to independently verify the claims due to the remoteness of and poor security in the area.

The Ghormach district, an ethnic Pashtun pocket in the mainly Tajik and Uzbek north, has seen a steady rise in violence in the last two years, holding up work on completion of a road linking the west to the capital, Kabul, and hampering aid deliveries.

Hundreds of Afghans have been killed in U.S. air strikes this year, leading to seething resentment against the presence of foreign troops and a rift between Karzai and his Western backers.

Some 4,000 people, more than a third of them civilians, have been killed this year in fighting with the Taliban, who have expanded the scope and scale of their insurgency to try to oust Karzai's Western-backed government and eject foreign forces.

NATO and U.S.-led coalition troops in Afghanistan say they do their utmost to avoid civilian casualties, but mistakes do happen. Hundreds of civilians are killed in Taliban attacks, especially by suicide and roadside bombs.

In a latest suicide attack near a government office, five people, three of them civilians, were wounded on Thursday in Maidan Wardak province, an official said. (Writing by Sayed Salahuddin; Editing by Valerie Lee)

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