The number of dead is almost as large as from a similar attack in December, which the same group claimed and was followed by tit-for-tat air strikes with neighbouring Pakistan.

The attacks occurred in Sistan-Baluchistan province which has for years faced unrest involving drug-smuggling gangs, rebels from the minority, and extremists.

“The case of the terrorist attacks was closed with the martyrdom of 10 members of the security forces,” and the killing of 18 “terrorists”, state television said.

Majid Mirahmadi, vice-minister of the interior, had earlier told the channel that five members of the Islamic Revolutionary Guard Corps and the police died during two night-time attacks against a Guards base in Rask and a police post in Chabahar.

“The terrorists had planned to seize military bases,” Mirahmadi later told state television, adding “none of them survived” the clashes.

He warned that the death toll could rise as some of the security forces injured in the attacks were “not in a favourable condition”.

He added that the assailants appeared to be foreigners, without providing further details.

The number of assailants killed in the clashes also rose from the 15 which General Mohammad Pakpour, who heads the Guards’ land forces, had announced on television.

The Jaish al-Adl (Army of Justice, in Arabic) group claimed the attacks on its Telegram channel.

Based in Pakistan, the rebel organisation, formed in 2012, is listed as a “terrorist” group by Iran and also by the United States.

Jaish al-Adl claimed an attack in December that killed 11 officers, one of the deadliest attacks in years, at a police station in Sistan-Baluchistan’s city of Rask.

The group claimed another police station attack in Rask that killed one officer on January 10.

A week later, Iran said it retaliated with missiles and drone strikes against Jaish al-Adl over the border in Pakistan. Pakistan then said it carried out air strikes against separatists inside Iran.

The Iranian strikes killed at least two children, according to Pakistan, while Pakistan’s strikes left at least nine people dead in Iran, according to the official IRNA news agency.

The rare cross-border fire added to regional tensions during the Israel-Hamas war in the Gaza Strip, but by late January the two countries sought to ease the pressure.

The porous border region of Baluchistan is split between Iran and Pakistan.