Britain’s ambassador to Saudi Arabia warned today that another terrorist attack in the kingdom was “probable”.

Tens of European, US and other hostages were released today and a gunmen believed to be the lead Islamic militant holding them was arrested, a Saudi security official said, adding that two other gunmen were “in the process of being arrested”.

Saudi security forces have stormed an expat housing complex where suspected Islamic militants are holed up with a reported 50 hostages after attacking oil company offices.

Saudi security forces stormed a prestige expatriate housing complex where gunmen holed up and took hostages after a shooting dead at least six people at oil company offices in the eastern city of Khobar.