WASHINGTON (Reuters) - President Barack Obama, in his first major military decision, has ordered 17,000 more U.S. troops to Afghanistan to tackle worsening insurgent violence, the White House said on Tuesday.

“This increase is necessary to stabilize a deteriorating situation in Afghanistan, which has not received the strategic attention, direction and resources it urgently requires,” Obama said in a written statement.

As a presidential candidate, Obama promised to focus more attention on the war in Afghanistan, where violence has risen dramatically in the past two years as Taliban militants and other insurgents have gained strength.

“The decision was communicated to the Pentagon yesterday. The orders were signed today,” White House spokesman Robert Gibbs told reporters traveling with Obama in Denver.

The 17,000 troops include an Army brigade equipped with Stryker armored vehicles, a Marine expeditionary brigade and support personnel, officials said.

The forces are part of an anticipated U.S. troop build-up that could expand the U.S. military presence in Afghanistan to 60,000 troops, from a current 38,000, in coming months.

There are also some 30,000 troops from NATO nations attempting to stabilize Afghanistan.

“There is no more solemn duty as President than the decision to deploy our armed forces into harm’s way,” Obama said. “I do it today mindful that the situation in Afghanistan and Pakistan demands urgent attention and swift action.”

The announcement comes while the White House is still conducting a broad review of U.S. policy on Afghanistan.

The deployment provides two of three extra combat brigades requested by top U.S. and NATO commander in Afghanistan, U.S. Army General David McKiernan.

The extra forces will go to southern Afghanistan, where a shortage of U.S. and NATO troops face an intensifying Taliban insurgency.

The units had originally been scheduled to go to Iraq and Obama’s said “the fact that we are going to responsibly drawdown our forces in Iraq allows us the flexibility to increase our presence in Afghanistan.”

A senior administration official said on Tuesday Obama will make a decision in weeks on cutting troop levels in Iraq, where the United States has 146,000 troops. Obama has pledged to pull out all U.S. combat troops from Iraq within 16 months, while shifting thousands of soldiers to Afghanistan.

Slideshow ( 3 images )

Both Democrats and Republicans welcomed Obama’s decision to send more troops to Afghanistan.

Sen. John McCain, the Arizona Republican defeated by Obama in last November’s presidential election, described the situation in Afghanistan as “dire.” But he also called on Obama to spell out a clear strategy.

“There still exists no integrated civil-military plan for this war -- more than seven years after we began military operations,” McCain said. “A major change in course is long overdue.”