British people should remain "vigilant" following a suspected terrorist attack in a busy shopping area of Stockholm, Home Secretary Theresa May has said.
Government officials are talking to Swedish authorities to learn the details of two explosions in the capital, she said.
Police in Sweden believe the blasts were caused by an apparent suicide bomber, who killed himself and injured two people.
A Swedish news agency said it received an email threat just before the attack that referred to the country's soldiers in Afghanistan and a cartoon of the Prophet Muhammad that outraged the Muslim world.
The UK terror threat level was raised from "substantial" to "severe" in January.
Mrs May told Sky News' Sunday Live: "The threat level in the UK remains at severe and that means that an attack is possible, indeed is highly likely.
"So it is right that everyone should be vigilant in the UK. We have a very high threat level from international terrorism here in the UK and as I say, people do need to be vigilant.
"Of course, the authorities here will be in touch with authorities in Sweden to learn what we can about what has happened there."
She added: "The Swedish government, as I understand it, has indicated that they believe this was a terrorist attack.
"But of course again we need to look at the details of it and we will be talking to them about the details of that attack."