President Bush on Thursday announced a surge in U.S. and NATO troops in Afghanistan and asked Congress for an additional $11.8 billion to pump up the Afghan army and help rebuild the country.

Currently, 27,000 U.S. troops are in Afghanistan — the highest number since the October 2001 invasion. The additional deployment follows a request made last month by Defense Secretary Robert Gates while he was visiting the top U.S. commander in that country.

About 3,200 forces from the 173rd Airborne Brigade, located in Vicenza, Italy, will deploy to Afghanistan beginning in spring 2007, according to the Department of Defense. The brigade was previously scheduled to deploy to Iraq, but will be going to replace the U.S. Army's 3rd Brigade from the 10th Mountain division, which was recently kept beyond its normal rotation to help beef up the number of forces on the ground.

"We cannot allow terrorists to gain sanctuary anywhere," Bush said at the American Enterprise Institute. "Our goal in Afghanistan is to help the people of that country defeat the terrorists and establish a stable, moderate, democratic state that respects the rights of its citizens, governs its territory effectively and is a reliable ally in this war against extremists and terrorists. I know to some it seems like an impossible task."

Bush said the government of Afghanistan, led by President Hamid Karzai, has made great strides in improving the lives of citizens — much to the dismay of the terrorists, who have increased their activities there.

"They watch our actions, they adjust their tactics, and in 2006, this enemy struck back with a vengeance as freedom began to spread," the president said.

Roadside bombs doubled, direct fire attacks tripled and suicide bombings nearly quintupled, he said. "These escalated attacks were part of a Taliban offensive that made 2006 the most violent year in Afghanistan since the liberation of the country."

NATO, which is leading military operations in Afghanistan, is 35,500-troops strong. It plans to go after the Taliban in the mountains of that country this spring, once the snow melts in the passes.

"The snow is going to melt in the Hindu Kush mountains and when it does we can expect fierce fighting to continue," the president said.

Bush also chided NATO nations that have hesitated to send additional troops or allow soldiers in Afghanistan to fight in the violent south and under other dangerous circumstances.

"When our commanders on the ground say to our respective countries 'We need additional help,' our NATO countries must provide it," Bush said. "As well, allies must lift restrictions on the forces they do provide so NATO commanders have the flexibility they need to defeat the enemy wherever the enemy may make its stand."

In addition to international military operations, Bush pledged to help increase the Afghan police to 80,000 officers, from 61,000, and the army to 70,000 soldiers, from 30,000, in 2008. The president said another goal would be to expand the amount of human intelligence to root out terrorists.

The buildup is likely to be better received on Capitol Hill than the new strategy in Iraq.

In his first news conference since before Christmas, Bush defended the Iraq buildup now under fire by most Democrats and some Republicans. He said lawmakers have a right to criticize the plan and noted the resolution the House is debating is nonbinding. He said there's no sign it has hurt troop morale but warned that others are listening.

FOX News' Wendell Goler and Nick Simeone contributed to this report.