Authorities in Afghanistan say that a powerful bomb explosion in a central province has killed 25 people, including at least 15 school children.  President Hamid Karzai has condemned the blast as a "savage and anti-Islamic attack."  The violence comes as thousands of U.S Marines are engaged in a major anti-insurgency offensive in the south of the country.  

The bomb explosion occurred in the central province of Logar and officials say that several policemen are also among those killed.

Afghan Interior Ministry spokesman Zamary Bashary tells VOA the explosive was hidden in a timber truck overturned on the side of the road the night before.  The bomb was detonated, he says, when local police arrived in the morning to check the abandoned vehicle.  

"We are really sorry to say that among those 25 people, 15 of them are school children who were getting in to their school and they saw the vehicle that was overturned and they just came nearby to see what is going on with the vehicle, which was detonated and unfortunately killed all of them in a very cruel and inhuman way," he said.

The number of people killed in the attack is the worst death toll from a single blast in Afghanistan this year.

Taliban insurgents have stepped up attacks on local and foreign targets in recent months, provoking NATO and U.S forces to launch a major offensive in the militant-dominated southern province of Helmand.  Thousands of U.S. Marines are involved in the assault, the biggest since international forces ousted the Taliban from power in late 2001.

Military commanders have not reported any major engagement with militants in Helmand.

But there is no let up in insurgent attacks on Afghan civilians and on local, as well as coalition forces across the country.  The violence has left up to 20 foreign troops dead in the past week, most of them from the United States and Britain.

NATO officials reported deaths of two more soldiers on Thursday in southern Afghanistan, but gave no other details.

Meanwhile, speaking to reporters in neighboring Pakistan, chairman of the NATO's military committee, Admiral Giampaolo di Paola described the offensive in Afghanistan's Helmand Province as an important step toward eliminating Taliban strongholds in southern parts of the country.  He says that Helmand Province is also known for producing most of the narcotics in Afghanistan that the NATO official says is feeding the Taliban terror activities.

"So now that we are going in to try to clear and hold [the ground] and to protect and allow the people of that region to live more safe, to have the freedom to go to vote, to have the freedom to go to schools, to have the freedom to send women in the activity they feel appropriate for women, well I think this is a very important step we are taking to dry down the breathing ground of terror," he said.

Afghanistan's southern provinces are seen as the center of the Taliban-led insurgency.  Coalition commanders believe some of the top Taliban leaders have taken refuge in the southwestern Pakistani province of Baluchistan, which borders southern parts of Afghanistan, but Pakistan denies the allegation.