US Army Patrol
US army on patrol by the ancient arches of Ashur, Iraq, in 2008 US Army

More than 50,000 personnel in the US Army could lose their jobs over the next two years as part of an exercise to downsize the largest branch of the armed forces, US media report.

Leaked documents seen by USA Today reveal the army is to reduce its size by 40,000 troops by 2017, with a further 17,000 civilian employees also facing layoffs.

The drastic cuts would reduce the number of active personnel in the army from the current level of 490,000 to 450,000 – the lowest since before the country's entry into the Second World War.

The downsizing had been on the cards after the Pentagon's budget, released in February, outlined a cut in the size of the army to 450,000 troops by 2018.

The news comes on the back of US President Barack Obama pledging increased military support for the moderate factions fighting Islamic State (Isis) militants in Syria.

But he ruled out sending in more American ground troops.

"We're intensifying our efforts against Isil's base in Syria. Our air strikes will continue to target the oil and gas facilities that fund so much of their operations," Obama said at the Pentagon on 6 July.

The proposed reduction in troops and civilians is due to budget constraints, USA Today said.

The army will have to slash a further 30,000 soldiers from its ranks if the automatic budget cuts known as sequestration come into effect in October.

The US army had about 570,000 active soldiers serving in its ranks during the peak of the fighting in Iraq and Afghanistan in 2012.