Tensions flare after twin attacks on 7 June on parliament and shrine of revolutionary leader Ayatollah Ruhollah Khomeini in Tehran
An Iranian fisherman was shot and killed on Saturday by the Saudi coastguard, which accused him of entering Saudi waters, Iran's interior ministry said, fuelling tensions between the regional rivals.
"Two fishing boats were in the Persian Gulf and strayed due to high waves. The Saudi coastguard say the boats entered Saudi waters and killed one of the fishermen," Majid Aghababaie, head of border affairs at the interior ministry, said in a statement published by Iranian media.
"We are pursuing this matter to determine if the Iranian boats had crossed the Saudi border or not, but the action of the Saudis does not comply with humanitarian and navigational principles," Aghababaie said.
"Even if the boats had entered Saudi waters, the coastguard were not authorised to open fire," Aghababaie added.
Foreign ministry spokesman Bahram Ghassemi issued a similar statement.
Saudi coast guard kills Iranian fisherman, according to Iran TV https://t.co/7LcqQQ2pOA
— Natasha Fatah (@NatashaFatah) June 17, 2017
Iran's official IRNA news agency later quoted Aghababaie as saying one of the boats was missing.
"We have no news concerning one of the boats," he said.
The incident comes amid increased tensions between Sunni-led Saudi Arabia and its arch rival Iran.
Iran and Saudi Arabia accuse each other of subverting regional security and support opposite sides in conflicts in Syria, Yemen and Iraq.
The tensions flared after twin attacks on 7 June on the parliament and the shrine of revolutionary leader Ayatollah Ruhollah Khomeini in Tehran in which 17 people were killed.
The Islamic State (IS) group claimed responsibility.
But Iran's elite Revolutionary Guard has accused Saudi Arabia of involvement in the attacks.
Iran's Intelligence Minister Mahmoud Alavi has also put the blame on Riyadh.
"Saudi Arabia is sponsoring terrorist groups in Iran," he said on Thursday.
Saudis blamed for attacks
Iranian Foreign Minister Mohammad Javad Zarif also pointed the finger at Saudi Arabia, during a visit to Norway this week.
"We have intelligence that Saudi Arabia is actively engaged in promoting terrorist groups operating on the eastern side of Iran in Baluchistan," Zarif said.
The incident also comes as the Gulf faces one of its worst diplomatic crises in years.
Earlier this month Saudi Arabia and several of its allies cut ties with Qatar, accusing it of supporting extremist groups, including some backed by Iran.
Qatar denies the allegations.
Iran has urged its Gulf neighbours to engage in a dialogue to resolve their dispute.
It also sent several planeloads of food to Qatar earlier this month after the Gulf countries cut off air links with Doha.
Saudi Arabia also sealed its land border with Qatar, which relies heavily on imports for food and raw materials.