Soldiers of the U.S. army's Gator Company and members of the Afghan National Army patrol a road along the Pesh Valley in Afghanistan on Monday. The United States is temporarily increasing the size of its army by 22,000 soldiers to handle the demands of the wars in Afghanistan and Iraq. (Tim Wimborne/Reuters)

The United States will temporarily increase the size of its army by 22,000 soldiers to deal with demands placed on the force by wars in Afghanistan and Iraq, U.S. Defence Secretary Robert Gates said Monday.

The U.S. army currently has a total troop strength of 547,000. Roughly 130,000 are serving in Iraq, while the troop numbers in Afghanistan will rise to 68,000 by the end of the year.

It's the second time since 2007 the army's size has been increased.

The pace of operations in Iraq and Afghanistan has swollen the ranks of injured and stressed soldiers, reducing the number of troops available for deployment, Gates noted.

Gates said the increased numbers will help reduce the pressures of multiple rotations, easing the unpopular practice of keeping soldiers on active duty past their enlistment dates.

"The cumulative effect of these factors is that the army faces a period where its ability to continue to deploy combat units [with enough troops] is at risk," Gates told a Pentagon news conference.

"This is a temporary challenge that will peak in the coming year and abate over the course of the next three years."

Gates added that it's possible the U.S. could decide to further boost its troop numbers in Afghanistan, a war U.S. President Barack Obama has declared as his country's top overseas military priority.

U.S. Gen. Stanley McChrystal, who took over as commander for all U.S. and NATO forces in Afghanistan last month — including more than 2,800 Canadians — is nearing the end of a 60-day review of the campaign's needs. The former U.S. commander in Afghanistan, Gen. David McKiernan, had said he needed an additional 10,000 troops, beyond the 68,000. The White House is expected to make the decision by the end of the year.

News of the increase comes as four U.S. soldiers were killed in eastern Afghanistan, making July the deadliest month for American troops in the country.

At least 30 U.S. soldiers have died so far in July, two more than the toll for June 2008, which had been the deadliest month for the American force in Afghanistan.

Four Canadian soldiers have been killed in Afghanistan in July, raising the total number of Canadians killed since the mission started to 125. Two aid workers and one diplomat have also died.

With files from The Associated Press