KABUL, Afghanistan - US President Barack Obama expressed "deep regret" to President Hamid Karzai over recent civilian deaths in military operations in Afghanistan during a call, Karzai's office said on Thursday.

On Wednesday, the US commander of international troops in Afghanistan, General David Petraeus, said he was "deeply sorry" after nine civilians died in a coalition air strike in Kunar province, northeast Afghanistan, on Tuesday.

Karzai says those who died were nine young children out collecting firewood and has warned that international troops in Afghanistan face "huge problems" if the "daily killing of innocent civilians" does not stop.

The Afghan president discussed the deaths with his US counterpart in a call on Wednesday, his office said in a statement, and told him that "increasing civilian casualties" posed a "serious problem".

Karzai has previously argued that such incidents can drain support away from his administration.

Obama "expressed deep regret over recent civilian casualties and said he has ordered his military officials to take the necessary initiatives to bring a reduction and end to civilian casualties", the statement said.

The US embassy in Kabul did not immediately comment on the call.

The deaths of ordinary Afghans in foreign military operations against the Taliban have been high on the political agenda in Kabul recently.

AFP