British demands answers from Russia

British Prime Minister Theresa May says it's 'highly likely' Russia was responsible for a nerve agent attack on a former spy and his daughter in Salisbury.

The UK government has concluded Sergei and Yulia Skripal were poisoned by a military-grade chemical developed by Moscow.

Earlier the Kremlin denied involvement, but the prime minister says there are only two possible explanations: "Either this was a direct act by the Russian state against our country, or the Russian government lost control of its potentially catastrophically damaging nerve agent and allowed it to get into the hands of others."

Russia's ambassador has been summoned to the UK Foreign Office, which wants answers by tomorrow.