KABUL, Afghanistan (AP) – Militants ambushed a bus carrying construction workers in the country’s volatile south Friday, killing 19 of the laborers, while Afghan and NATO forces said they killed 35 Taliban militants in two separate firefights.

The attack on the bus in Kandahar province began when a roadside bomb exploded near the vehicle, said Zemeri Bashary, the Interior Ministry spokesman. Some laborers may have been killed by the bomb, while others were shot by militants who attacked the panicked workers with gunfire, he said.

Nineteen construction workers were killed and three wounded, Bashary said. It wasn’t immediately known how many people were on the bus or who the laborers worked for.

The attack, in Shorabak district, occurred in a remote area of southern Kandahar province that borders Pakistan some 110 miles south of Kandahar city.

Southern Afghanistan has seen a surge of violence this year, fueled by a resurgent Taliban and a growing drug trade. Afghan officials say that Taliban fighters cross the border from northern Pakistan to launch attacks in Afghanistan.

President Hamid Karzai, on a trip to Canada, condemned the attack and said that “heinous acts of terrorism” wouldn’t hinder his country’s reconstruction process.

In neighboring Uruzgan province, police Thursday evening killed 25 Taliban militants in a battle in Chorah district, about 200 miles southwest of Kabul, said provincial police chief Gen. Kasam Khan.

One policeman was killed and five were wounded, he said. Khan said police recovered the bodies of the militants.

NATO forces and Afghan police also fought Taliban militants in nearby Helmand province, killing 10 of the fighters, NATO said. One Afghan policeman was killed, said Ghulam Rasool, the Garmser district police chief.

President Bush, who met Friday with Pakistani President Gen. Pervez Musharraf in Washington, has repeatedly praised Pakistan for arresting hundreds of al-Qaida operatives inside its borders. But the United States has also urged Pakistan to do more to stop militants from crossing from its tribal regions into Afghanistan.

Pakistan earlier this month signed a truce with tribal figures, a move that Afghanistan has protested.

Bush will have talks Tuesday with Karzai. Then, he’ll have a three-way meeting with both leaders Wednesday.

In Brussels, Belgium, meanwhile, the EU’s special envoy to Afghanistan backed calls by NATO commanders to send up to 2,500 more troops to the southern provinces, saying it was vital to push for a quick military victory over the Taliban there.

Francesc Vendrell said the European Union and other international donors had to be quicker in helping establish quality local administrators and speedy aid to reconstruction aid to areas secured by the NATO military forces.

NATO’s top commander, Gen. James L. Jones, has appealed for up to 2,500 extra troops to join the 8,000 allied force battling stronger-than-expected Taliban resistance in the southern sector, but nations have been slow coming forward. On Wednesday, Jones indicated offers of more troops were coming.

NATO has about 20,000 troops in Afghanistan, while the United States has another 21,000 troops here, mostly in the east along the border with Pakistan.