Washington ? Fresh U.S. combat casualties show the continuing danger five months into the anti-terror campaign in Afghanistan even as the Pentagon prepares to expand it to other countries.

In one of the largest joint operations of the war, a U.S.-led force of 1,500 Afghan allies, U.S. special forces and troops from the Army’s 101st Airborne assault troops assembled for a battle that began Friday night against regrouping Taliban and al-Qaida, a U.S. defense official said Saturday.

The Pentagon said one American and two Afghans allies were killed, and that an unspecified number from each country were wounded.

Afghan fighters interviewed in Gardez, in eastern Afghanistan, said Americans told them there were about 4,000 al-Qaida and Taliban warriors holed up in the mountains.

For the first time, warplanes dropped newly developed bombs designed to send suffocating blasts through cave complexes, military officials said. The “thermobaric” bombs were tested in December and officials said in January that they would be rushed to the region for the war.

The battle was yet another example of how hard it is to stamp out the terrorists and their supporters in Afghanistan, months after the Taliban abandoned their stronghold of Kandahar and al-Qaida fighters were pushed from Tora Bora – what at that time was called their last stronghold.

“We’ve said all along that it is not over,” Pentagon spokeswoman Victoria Clarke said hours before the bombing began.

More than a week of bombing to destroy caves and ammunition was needed in January at a huge cave complex at Zawar Kili – also after the discovery that enemy figures had been regrouping there.

President Bush learned of the combat death of the death of the American soldier from Condoleezza Rice, his national security adviser, while at Camp David, the presidential retreat in western Maryland, a White House spokesman said.

The new assault at Gardez came at the end of a week in which U.S. officials said Bush was planning to send troops to Yemen and the former Soviet Republic of Georgia, expanding the number of countries into which special forces are training local militaries to fight terrorism.

Administration officials said Friday that Bush had given the go-ahead to dispatch U.S. troops to Yemen. A Yemeni official said Saturday that he expects 100 Americans to arrive soon to train 2,000 Yemeni military personnel at a coast guard training center to be built in Aden.

That is the of the October 2000 attack that killed 17 American sailors on the USS Cole.

Washington has been pushing Yemen for greater cooperation against terrorism since the suicide bombing, which like the Sept. 11 attacks on America, was blamed on Osama bin Laden’s al-Qaida network.

Officials said last week that as many as 200 Americans would deploy to help train the military in Georgia, amid sketchy reports terrorists have taken refuge in the Pankisi Gorge near Georgia’s border with Russia’s breakaway region of Chechnya.

Last month, 160 special forces troops, were sent to the Philippines to help train local armed forces battling the Muslim extremist Abu Sayyaf group, which has been loosely linked to al-Qaida.