Following the Manchester bombing MI5 has raised the UK's terror threat level to "critical", the third time it has reached the top rating since its inception. Meanwhile, as the map below shows, there are now more than 45 countries around the world where the Foreign Office believes a terror attack is "very likely" to be attempted.
They include Germany, whose capital witnessed a deadly attack at a Christmas market in December, as well as France, Turkey and Belgium. The Paris terror attacks in November 2015 saw 130 killed, while in July last year 84 people died when a truck was driven through a crowd of people on the promenade in Nice.
Turkey witnessed a string of attacks last year, most notably at Istanbul's Atatürk Airport, but also in the capital, Ankara, and the city of Gaziantep. The Brussels attacks in March 2016, meanwhile, saw 32 people killed.
The top terror threat level is also given to Egypt, where a Russian aircraft was bombed in 2015, Tunisia, where 30 Britons were killed in a massacre during the same year, Indonesia, Russia, Myanmar, Kenya, the Philippines, Colombia, Thailand and Australia. The inclusion of much of the Middle East, including Iraq, Saudi Arabia, Yemen, Syria, Lebanon, Israel and Afghanistan, will come as no surprise.
Last year the terror threat level increased in 12 countries: Qatar, Kuwait, Tanzania, Senegal, Ghana, Burkina Faso, South Africa, Oman, Sierra Leone, Guinea, Liberia, Mozambique, and did not fall in a single destination.
So far this year it has increased in five countries: Kosovo, Mauritius, Singapore, the United States and Zambia, but has fallen in Ethiopia, Greece and Ireland.
The Foreign Office traditionally uses four ratings when judging the threat of a terrorist attack in its travel advice: high, general, underlying and low. However, it recently reworded its advice for the top threat level, stating that "terrorists are very likely to try to carry out attacks" in applicable countries.
Countries where the terror threat is low include Iceland, Bolivia, Ecuador, Poland, the Czech Republic, Switzerland, Hungary, Vietnam and Japan.