Unidentified gunmen have killed three Iranian police on patrol in the northwest of the country near the border with Iraq, the Mehr news agency reported on Wednesday.
Tuesday night's attack comes after the authorities in Shia-ruled Iran beefed up security along the frontier in response to a Sunni militant offensive that has captured swathes of Iraqi territory.
The police were killed near the village of Taze-Abad, about 50 kilometres (30 miles) from the border with Iraq, said Mehr.
An official familiar with the attack denied the Islamic State of Iraq and the Levant (ISIL) carried out the attack, or that the jihadist group leading the offensive in Iraq had entered Iran.
The attack comes just days after the Iranian army clashed in the same region with suspected forces of the Party of Free Life of Kurdistan (PJAK).
The clash, which took place on Saturday, killed at least one member from the ranks of the PJAK, the main Kurdish armed movement opposed to Tehran based in northeastern Iraq, media reports said.
Iran supports the Iraqi government of Shia Prime Minister Nuri al-Maliki in its fight with the Sunni militants who have seized control of vast stretches Iraqi territory since June 9, including second city Mosul.