Iran demanded an explanation from Turkey yesterday after Turkish warplanes reportedly bombed a Kurdish area of north-west Iran, killing five people and wounding 10.
Tehran warned it could retaliate and overnight summoned the Turkish charge d'affaires to the foreign ministry for the second time in a week amid rapidly rising tensions between the countries.
The foreign ministry warned of the "consequences of this aggression" and demanded "formal apologies, convincing explanations and a pledge to repair the damage", according to the state news agency IRNA.
In Ankara, Turkish officials said an investigation had begun into the alleged bombing. "Has the incident really happened? Why and how has it happened? I believe it to be suitable to make an announcement after looking into these points," the Turkish Defence Minister, Mr Sabahattin Cakmakoglu, told reporters.
"We are currently collecting information," he added.
Iranian officials said Turkish jets bombed a military outpost on Sunday in the mainly Kurdish town of Piranshahr, along the border with Iraq, as well as surrounding areas. Five people were killed, including a member of the elite Revolutionary Guard.
"It has now become a habit of Turkey to create problems for Iran," said the conservative Tehran Times, repeating charges that Ankara was behind the violent student riots in the Iranian capital last week.
The charge d'affaires, Mr Kut Sezgin, was summoned to the foreign ministry last Wednesday after the Turkish Prime Minister, Mr Bulent Ecevit, said student unrest was a "natural" reaction to Iran's "oppressive regime".