Karzai issues warning to Pakistan
Afghan President Hamid Karzai has threatened to send troops over the border into Pakistan to confront militants based there.
He said that when militants crossed over from Pakistan to kill Afghans and coalition troops, his nation had the right to retaliate in "self-defence".
Mr Karzai's remarks came two days after Taleban fighters attacked an Afghan jail, freeing hundreds of prisoners.
Pakistan warned it would not tolerate outside interference in its affairs.
Yusuf Raza Gilani, Pakistan's prime minister, said the border between their two countries was too long to police.
"Neither do we interfere in anyone else's matters, nor will we allow anyone to interfere in our territorial limits and our affairs," he told the Associated Press news agency.
"We want a stable Afghanistan. It is in our interest. How can we go to destabilise our brotherly country?"
Pakistan denies providing a safe haven for the Taleban or other militants.
Mr Karzai has long pleaded for Pakistan and international forces to confront militants in Pakistan but has never before threatened to send troops over the border.
The BBC's Quil Lawrence in Kabul says it is the strongest language yet from Mr Karzai on his neighbour.
But while the Afghan president is using more provocative language than before, it remains to be seen whether this leads to more robust action, our correspondent says.
Mr Karzai's news conference had been intended to focus on this week's Afghan donors' conference in Paris, at which world powers pledged about $20bn (£10bn) to help re-build his country.
But instead, it was dominated by the prison break that led to the escape of some 900 inmates, including 350 Taleban members, and Afghanistan's response to militant attacks.
Mr Karzai said: "Afghanistan has the right of self-defence. When they cross the territory from Pakistan to come and kill Afghans and to kill coalition troops it exactly gives us the right to go back and do the same."
He warned that he was prepared to seek out Taleban leaders wherever they were, specifically naming Baitullah Mehsud, who is based in South Waziristan, Pakistan.
"Baitullah Mehsud should know that we will go after him now and hit him in his house," Mr Karzai said, adding that Taleban leader Mullah Omar could expect the same.
He went on: "This is a two-way road in this case and Afghans are good in the two-way road journey."
Some 20 escapees from Kandahar prison have been recaptured in the manhunt by Afghan and international troops, according to Afghan officials.
Nato said at least 17 insurgents had been killed but did not confirm whether any fugitives from the jail were among the dead.
The US military said those killed were hit by an air strike after being found at a farm in Kandahar with a cache of weapons.
A former Taleban stronghold, Kandahar is one of the key battlegrounds in the insurgency against President Karzai and troops from Nato and a US-led coalition.