Two sets of South African siblings have appeared in court on terror-related charges, including a pair of twin brothers accused of plotting to blow up the US Embassy and various Jewish institutions in the country.

The four were allegedly planning to fly to Syria, where they were due to undergo training by a terror organisation, police spokesman Hangwane Mulaudzi said. They had been under surveillance for nearly a year.

“The allegation is that after the training, they would come back to South Africa,” Mr Mulaudzi said, adding that security officials hoped there would be more arrests.

Twin brothers Brandon-Lee Thulsie and Tony-Lee Thulsie were charged with conspiring to blow up the US Embassy in Pretoria and various Jewish targets. Mr Mulaudzi said the twins were arrested in Johannesburg on Saturday.

A provisional charge sheet says the brothers may have links to Islamic State.

Siblings Fatima Patel and Ibrahim Mohammed Patel appeared in a separate court on Monday after a stun grenade and live ammunition were confiscated during a raid on their home outside Johannesburg on Saturday night, said Phindi Louw, a spokeswoman for the National Prosecuting Authority.

All four of the accused are expected to have the chance to apply for bail next week.

Mr Mulaudzi said the arrests are not connected to the warning the United States issued last month of possible terror attacks in South Africa during the holy month of Ramadan.

The South African government accused Washington of creating unnecessary alarm and undermining the country’s fight against terror.

This is not the first time South Africa has arrested someone suspected of trying to leave to join Islamic State.

Last year, a 15-year-old girl was arrested on a flight in Cape Town while on her way to join the extremist group, the state security ministry said. It was the country’s first known detention linked to Islamic State.