U.S. President Donald Trump has said that the American military is considering tough measures against Iran, including the possibility of military intervention. Speaking to reporters aboard Air Force One on Sunday night, Trump stated that the issue is being taken very seriously and that strong options are under review. He added that Iranian leaders have called for talks following the threat of military action, and a meeting is being arranged, though action could occur before any talks take place.

Trump’s latest warning comes as Iranian leaders have issued stern cautions against any foreign military intervention. Iranian Parliament Speaker Mohammad Bagher Ghalibaf warned that if Iran is attacked, both Israeli-held territories and all U.S. bases and ships would become legitimate targets. The tensions follow widespread protests that began on December 28 when Tehran’s Grand Bazaar merchants shut their shops over the falling value of the rial.

According to Iranian state media, at least 109 security personnel have been killed in the unrest. Authorities have not confirmed the number of civilian casualties, but opposition activists abroad claim the death toll is much higher and includes hundreds of protesters.