LONDON (Reuters) - Britain has told its citizens traveling to Russia to be aware of anti-British sentiment and harassment and avoid commenting on politics, as relations between the two countries sour over the poisoning of a former Russian double agent.

The Foreign Office updated its travel advice on Wednesday after Prime Minister Theresa May said Russia was behind the attack on Sergei Skripal and his daughter with nerve agent, and expelled 23 diplomats. Russia denies responsibility.

“Due to heightened political tensions between the UK and Russia, you should be aware of the possibility of anti-British sentiment or harassment at this time,” the Foreign Office said in a travel advisory.

“You’re advised to remain vigilant, avoid any protests or demonstrations and avoid commenting publicly on political developments,” it added.

British police have estimated that 10,000 to 20,000 British soccer fans were expected to travel to Russia in the Summer for the finals of the World Cup.