Air strikes were the main culprit responsible for the increase in civilian casualties U.S. Air Force/Getty Images KABUL (Reuters) - Civilian casualties from Afghan and American air strikes have risen more than 50 percent since last year, the United Nations said on Thursday, as troops increase attacks on militants under a new strategy announced by U.S. President Donald Trump in August.

As of the end of September, at least 205 civilians had been killed and 261 wounded this year in air strikes in Afghanistan, U.N. investigators said in a quarterly report.

At least 38 percent of those casualties were caused by international military forces, while the majority were attributed to the Afghan Air Force, which has begun to conduct more attacks on its own.

More than two thirds of the civilian victims were women and children, the report said.

In September, U.S. warplanes dropped more bombs than in any single month since 2010, driven largely by Trump's strategy of trying to reassert pressure on militants after several years of drawdown by foreign troops.

A spokesman for the U.S. military command did not immediately comment on the report.

General Dawlat Waziri, spokesman for the Afghan Ministry of Defence, rejected the findings and said the government took civilian casualties seriously.

"It is quite obvious that Taliban and other insurgent groups cause more civilian casualties," he said, adding that insurgents also "use civilians as human shields and hide in residential areas".

Overall civilian casualties decreased slightly compared to the same period last year, the report said.

At least 2,640 civilians were killed and 5,379 injured this year, compared to 2,616 killed and 5,915 injured in the same period of 2016.

The drop reflected fewer casualties from fighting in populated areas, the report noted, as militants failed to capture any major cities.

The head of the U.N. mission in Afghanistan, Tadamichi Yamamoto, praised the Afghan government for formally endorsing a national policy designed to reduce civilian casualties.

"The government owes it to its citizens, particularly the victims of the armed conflict, to ensure full implementation of the policy through a concrete action plan," he said.

Overall the U.N. attributed 64 percent of civilian casualties to anti-government militants like the Taliban and Islamic State.

Pro-government forces were responsible for 20 percent overall, while the remainder was attributed to joint fighting or unidentified groups, according to the U.N.

(Reporting by Josh Smith; Editing by Nick Macfie)