The United States has issued a new terror alert for its citizens traveling to Europe this summer in light of recent terror attacks in Britain, France and Sweden.
The state department cited the Westminster attacks in March as evidence of the ability of the Islamic State of Iraq and the Levant "to plan and execute terrorist attacks in Europe".
In March, Khalid Masood drove a car into pedestrians on Westminster Bridge, killing four people, before stabbing a policeman to death inside the Palace of Westminster grounds.
Last week, armed police arrested a terror suspect as he headed towards Downing Street with bag packed with knives.
The US state department said it was concerned that "terrorist sympathisers or self-radicalised extremists" could carry out attacks at any time, with no warning.
The alert said US citizens should be especially vigilant at large, high profile events, particularly at tourist sites during the summer travel season.
The state department's previous travel alert for Europe was issued last November and expired in February. It focused on the threat in Europe at winter holiday festivals, events, and outdoor markets.