LONDON (Reuters) - Saudi Arabia has freed three Iranian fishermen detained by the kingdom’s coastguard last year, Iran’s state news agency IRNA quoted an Iranian official as saying on Tuesday, following negotiations between the two regional rivals.

Tension between Shi’ite Iran and Saudi Arabia’s conservative Sunni monarchy has run high in recent years. The two countries have backed opposing forces in wars across the Middle East, usually along sectarian lines.

Ardeshir Yarahmadi, the head of the fisheries department of Iran’s Bushehr province, said the three fishermen were arrested in June 2017 after their boat drifted into the Saudi waters.

They had been freed this week after “negotiations between foreign ministry officials of both countries”, Yarahmadi said, without giving the date of their release.

In February, Saudi Arabia freed nine Iranian fishermen detained for two years, accusing them of entering its waters.

Saudi authorities could not immediately be reached for comment. The country broke all ties with Iran in 2016.