The Navy of Iran’s Islamic Revolution Guards Corps (IRGC) has seized a Saudi vessel after trespassing on the Islamic Republic’s territorial waters in the Persian Gulf.

The vessel, which had set off from the Saudi port of Dareen, was seized in the waters off the southern Iranian province of Bushehr on Friday, an informed source told Fars news agency.

The source added that all of the vessel crew were detained and that investigations are underway.

Iranian security forces see it as a principle to safeguard the Islamic Republic’s territorial waters and will not allow anybody to trespass on Iran’s waters, the source said.

Last month, the Iranian Interior Ministry’s director general for border affairs Majid Aqa-Babaei said that Saudi Arabia’s coastguard had opened fire on Iranian fishing boats in the waters south of Iran and killed a fisherman.

The incident happened after two Iranian boats fishing in the Persian Gulf strayed from their course due to big sea waves, Aqa-Babaei said on June 17.

Relations between Iran and Saudi Arabia worsened after a deadly human crush occurred during Hajj rituals in Mina, near Mecca in September 2015.

Islamic Republic officials blamed the incompetence of Saudi officials for the incident, which, according to Iran, killed 4,700 people, including 465 Iranian nationals.

Earlier that same month, a massive construction crane had collapsed into Mecca’s Grand Mosque, killing more than 100 pilgrims, including 11 Iranians, and injuring over 200 others, among them 32 Iranian nationals.

Mutual ties deteriorated further when Riyadh executed prominent Saudi Shia cleric Sheikh Nimr al-Nimr in January 2016. Saudi Arabia unilaterally severed its diplomatic ties with Iran after protests in front of its diplomatic premises in the cities of Tehran and Mashhad against Nimr’s execution.