At least one person has been killed and three others wounded in an attack by unidentified gunmen on an Iranian bus travelling in eastern Turkey.

Iran’s official news agency IRNA quoted Hossein Qassemi, the Iranian consul general in the city of Erzurum, as saying that one person died after succumbing to the wounds he had received to his head. Qassemi said the identity and nationality of the victim “is not known yet,” adding that all other passengers are in good condition.

The report said Iran's Consulate in Erzurum is investigating the issue, adding that no group has claimed responsibility for the attack yet.

However, Turkey’s official Anadolu news agency attributed the assault to Kurdistan Workers' Party (PKK) militants, saying an Iranian national and a Turkish sergeant had died following a shooting at an Iranian bus travelling in the highway linking Dogubayazit in Agri Province to Caldiran in Van Province.

The attack was carried out at about 11:30 a.m. local time (0830 GMT) in the Somkaya area near the village of Cetenli, Anadolu said, adding that PKK militants blocked the highway by setting fire to three 18-wheelers and two trucks. That was followed by a shooting attack on a passing Iranian bus, according to the Turkish news agency's account, where one person was killed and three others were injured.

Militants set fire to three 18-wheelers and two trucks, blocking the highway linking Dogubayazit in Agri Province to Caldiran in Van Province, August 7, 2015.

Special forces were then dispatched to the scene of the attack, prompting the militants to begin a gunfight which lasted about two hours and killed the Turkish sergeant.

The injured passengers and crew in the bus have been taken to a hospital in Dogubayazit. An image carried by Anadolu showed the bus carrying an Iranian license plate, with the combination of the digits showing that it was registered in the province of East Azerbaijan, which is located close to the Turkish border in northwestern Iran.

Anadolu also reported earlier on Friday that at least three people were killed in a fresh gunfight in southern Turkey, after supporters of the PKK fired shots at police officers and workers in the vicinity of the town of Silopi, located near Turkey’s border with Iraq.

The PKK, which seeks to gain self-rule, has been engaged in militancy in southeastern Turkey for decades. A shaky ceasefire between Ankara and the militants that had stood since 2013 was declared null by the PKK following Turkish airstrikes against the group in the wake of a bomb attack in Suruc, southern Turkey.