Kabul, Afghanista ? A suicide bomber drove a motorbike into a crowd at a wrestling match in an Afghan border town Monday, killing 20 people. It was the third deadly bombing in a little over 24 hours in the Taliban’s former stronghold province of Kandahar.

The assault came shortly after a bomb targeted a truck convoy of Afghan soldiers in Kandahar city, killing four people and wounding 16. On Sunday, a suicide car bomber in that southern provincial capital killed a senior Canadian diplomat and two Afghan civilians.

The attack on the wrestling match in Spinboldak was the bloodiest yet in a string of two dozen suicide bombings in the past four months. It is a relatively new tactic for militants here and has stoked fears of an escalating siege of bloody attacks like those in Iraq.

Earlier Monday, President Hamid Karzai warned that Afghanistan could again become a staging post for terrorist strikes on Europe and America if international support wavers.

In Spinboldak, a key crossing point into Pakistan, a man with explosives strapped to his body blew himself up after riding a motorbike into the midst of about 100 wrestling fans watching a bout at a fair marking the Muslim holiday of Eid al-Adha.

“The motorcycle went up into the air in flames,” said Abdul Samad, who was in the crowd and fled with hordes of panicked spectators. “It was like doomsday … Some did not have their hands; others had their legs missing.”

Najamuddin, a 24-year-old wrestler who goes by only one name, was among the wounded treated at hospital in Chaman, Pakistan. The explosion seared his hair, beard and left arm, and he broke his right hand when he was blown to the ground.

“The explosion tossed me into the air and threw me back. When I got up, I saw people lying in blood,” Najamuddin said from his hospital bed.

Kandahar Gov. Asadullah Khalid put the toll at 20 dead and at least 30 wounded. Rafiq Tarin, a Pakistani official in Chaman, said more than 30 people were treated at the hospital there, including many in critical condition.

Khalid repeated an Afghan government claim that suicide attackers are being trained in Pakistan’s frontier region, a tribal area where Taliban loyalists and al-Qaida militants are thought to be hiding.

Pakistan’s government says it is trying to root out Islamic extremists. But officials on both sides acknowledge it is relatively easy for militants to cross back and forth along the mountainous border between the two countries.

Qari Mohammed Yusaf, who claims to speak for the Taliban, although his exact ties to the group’s leadership are unclear, said its fighters had planted the bomb that struck the Afghan army convoy in Kandahar city, but denied involvement in the Spinboldak attack.

“The Taliban didn’t do this suicide attack. We are targeting coalition and government forces but we are not targeting civilians,” he said in a phone call from an undisclosed location to an Associated Press reporter in Afghanistan.