U.S. military successes in Iraq have forced sophisticated and well-trained insurgents to pour into Afghanistan instead, part of the reason violence has spiked in Afghanistan, the Afghan defense minister said Tuesday.

In a demonstration of the increasingly deadly attacks, a roadside blast in the east where U.S. soldiers operate killed three NATO troops, while two separate roadside bombs in the south killed 16 Afghan civilians, officials said.

The Afghan defense minister, Gen. Abdul Rahim Wardak, said terrorists who would have once fought in Iraq have been "diverted" to Afghanistan.

"The success of coalition forces in Iraq and also some other issues in some of the neighboring countries have made it possible that there is a major increase in the foreign fighters," Wardak told a news conference. "There is no doubt that they are (better) equipped than before. They are well trained, more sophisticated, their coordination is much better."

The top U.S. commander in eastern Afghanistan, Maj. Gen. Jeffrey Schloesser, told The Associated Press last month that he is seeing a spike in the number of foreign militants — including Arabs and Chechens — flowing into Afghanistan. He said militant Web sites have been encouraging fighters to go to Afghanistan instead of Iraq.

"I can't prove they are coming from Iraq to Afghanistan, but I've seen it on Web sites that that's what they're being told to do," Schloesser said.

The Iraqi insurgency at its height drew Arab extremists and other jihadi leaders who were once focused on Afghanistan, including the Egyptian Abu Ayyub al-Masri, believed to be the current leader of al-Qaida in Iraq. Iran also stepped up aid to Shiite militias as sectarian strife grew after 2006. But the precise number foreign fighters in Iraq was never clear and many U.S. commanders believe local Iraqis comprise the bulk of the al-Qaida and other jihadi forces.

In Afghanistan, militant attacks have turned deadlier and more sophisticated this year, part of the reason more U.S. and NATO troops have died there in 2008 than in any year since the 2001 U.S.-led invasion.

NATO said a roadside bomb blast killed three of its soldiers in eastern Afghanistan Tuesday. The alliance did not provide their nationalities or the exact location of the blast, but the majority of troops in the east are American.

In the south, a bomb attack apparently intended for NATO troops exploded against an Afghan minivan in Uruzgan province, killing nine civilians, said Juma Gul Himat, the provincial police chief.

Himat blamed "the enemies of Afghanistan" — a term commonly used for the Taliban. He said the road where the bomb exploded is often used by NATO troops. The taxi had been traveling toward the provincial capital.

A second bomb blast also intended for NATO troops killed seven civilians traveling in a bus in Ghazni province on Monday, the Defense Ministry said Tuesday.

Most bomb attacks in Afghanistan are intended for Afghan or NATO soldiers, but the blasts are far more likely to kill civilians.

Violence has risen steadily in Afghanistan since late 2005. More than 4,700 people — mostly militants — have been killed in insurgency related-violence this year, according to an Associated Press count of figured provided by Afghan and Western officials.

Elsewhere, U.S.-led troops killed five insurgents in central Ghazni province on Monday during a raid to disrupt a foreign fighter network, the coalition said Tuesday.

The coalition also said one of its service members was killed and several others were wounded in southern Afghanistan on Monday when their vehicle was hit by a roadside bomb. No other information, including the service members' nationalities or precise location of the attack, was released.