Kabul, Afghanistan — Afghanistan threatened to mount cross-border raids into Pakistan yesterday when President Karzai insisted on his country’s right to “self defence.”

Leaders of the Taliban insurgency in southern and eastern Afghanistan are known to be based in the lawless Tribal Areas inside Pakistani territory and along the country’s north-west frontier. The self-proclaimed leader of the Pakistani Taliban, Baitullah Mehsud, has publicly ordered his followers to cross the border and attack NATO forces inside Afghanistan.

Mr. Karzai said Afghanistan had every right to respond. “When they cross the territory from Pakistan to come and kill Afghans and to kill coalition troops it gives us the right to go back and do the same.”

The president delivered a specific warning to Mr. Mehsud, who has become Pakistan’s most prominent extremist, and Mullah Mohammed Omar, the leader of the deposed Taliban regime who is also believed to have found sanctuary across the border. “Baitullah Mehsud should know that we will go after him now and hit him in his house,” Mr. Karzai said. “And the other fellow, Mullah Omar of Pakistan should know the same.”

Mr. Karzai added: “This is a two-way road. And Afghans are good at the two-way road journey. We will complete the journey and we will get them and we will defeat them. We will avenge all that they have done to Afghanistan for the past so many years.”

Pakistan’s new government has agreed a cease-fire with Taliban militants in the Tribal Areas and negotiations are continuing. Afghan officials and NATO commanders say these deals usually result in more cross-border attacks into Afghan territory. Incidents of this kind rose by 50% in April, according to NATO officials.

But NATO forces and America’s separate counter-terrorism operation have also been more active in frontier region. Unmanned drones have conducted a series of air strikes inside Pakistani territory.

Pakistan’s prime minister, Yousuf Raza Gilani, said his country desired only good relations with “brotherly” Afghanistan. He said no one could prevent all movement across the 1,500 mile frontier “even if Pakistan puts its entire army along the border.”

Mr. Karzai said the storming of the main jail in Kandahar by Taliban fighters, in which 450 prisoners escaped, was evidence of the country’s need for continued international assistance. The incident was “indicative of the weaknesses that we still have.” “Therefore it’s all the more reason for us to work harder and keep building Afghan institutions and intelligence and to be a lot more alert and steadfast in our resolve in confronting terrorism,” he said.

A state of emergency was declared in Kandahar as an operation was launched to hunt down the escaped prisoners. Fifteen Taliban fighters were reported to have been killed in an American-led operation, which included air strikes.