Afghan President Hamid Karzai has threatened to attack Taliban militants on Pakistani soil, saying his war-torn country had a right to do so out of 'self-defence'.
The warning came just days after US-led forces carried out an air strike in Pakistan's border area with Afghanistan.
The US says it was targeting militants, but Pakistan says 11 of its soldiers were killed.
It also came two days after more than 1,100 prisoners including hundreds of militants escaped from a jail in southern Kandahar.
'Afghanistan has the right to destroy terrorist nests on the other side of the border in self-defence,' Mr Karzai told a news conference in Kabul.
'When they cross the border from Pakistan to come and kill Afghans and coalition troops, it gives us exactly the right to go back and do the same,' he added, in his toughest comments yet on stamping out militancy along the border.
The stark warning earned a swift response from Pakistani Prime Minister Yousuf Raza Gilani, who said that his country would not tolerate any violations of its territorial sovereignty.
'We will neither interfere in the internal affairs of any country, nor will we allow anyone to interfere in our affairs,' Mr Gilani said.
'Such statements will not help in the normalisation of friendly relations between the two countries,' Mr Gilani said.
Mr Karzai's government suffered a blow on Friday when Taliban militants blasted open the prison in Kandahar city, freeing more than 1,100 prisoners including hundreds of insurgents, according to NATO-led forces.
At least 27 insurgents were killed as Afghan and international troops hunted for the escapees, police and troops said, but it was not immediately clear if they were escaped prisoners.
So far, 20 escapees have been recaptured, police say. Nine guards and a child were killed in the prison raid.
