The US embassy in Azerbaijan was on full alert on Monday after security forces in the oil-rich republic said it had been the target of a planned attack by a group of radical Islamist fighters captured outside Baku, the capital, at the weekend.

Azerbaijan’s ministry of national security said it had prevented a “large-scale horrifying attack against government structures and diplomatic missions” including the US embassy in Baku. The security forces conducted a swoop near the village of Mashtagi about 20 miles from Baku early on Saturday morning.