Russian billionaire Roman Abramovich can enter Britain on a visitor visa after gaining Israeli citizenship, Theresa May's spokesperson has said.

The Chelsea FC owner "can come as a visitor for six months but will need a visa to live, work or study in the UK," the spokesperson added.

The clarification came after Mr Abramovich was granted citizenship in Israel after failing to renew his visa to Britain.

Russia's 11 richest man's UK visa application had been "taking longer than usual" to process amid increasing tensions between London and Moscow, sources told Reuters.

It has been reported that Mr Abramovich would have to explain the source of his wealth to receive a new British visa.

Chelsea owner with Russian President Vladmir Putin

Commenting on his new Israeli citizenship, the Kremlin said Mr Abramovich had every right to take it under Israel's 'law of return' for Jews.

"The Kremlin doesn't think anything about this," government spokesman Dmitry Peskov said.

"An entrepreneur has received Israeli citizenship. So what? It is his right."

Mr Abramovich, who is Jewish, flew to Tel Aviv on Monday and obtained documents confirming his status as an Israeli citizen, the Israeli news site Ynet reported.

The country's interior ministry confirmed Mr Abramovich had gained citizenship there, The Times of Israel reports, adding that he is now the country's richest man.

An official at Nativ, a government department that deals with Jewish communities in the former Soviet Union, said Mr Abramovich had applied for an immigration visa at Israel's embassy in Moscow.

They added: "His documents were examined under the 'law of return' and he was indeed entitled to immigrant status in Israel, and as a result he was issued an immigration visa."

Israel's law of return gives every Jew, or child or grandchild of a Jew, the right to Israeli citizenship.

Relations between Moscow and London have been strained since the poisoning of former Russian double-agent Sergei Skripal in Salisbury in March.

Britain has blamed the attack on Russia but the Kremlin denies any involvement.

The UK said this month it would review long-term visas of wealthy Russians after the poisoning.

Mr Abramovich has been a regular visitor to Israel and Ynet said he had bought a property that was formerly a hotel.

The building is based in an old Tel Aviv neighbourhood close to the Mediterranean shore.

The Sunday Times Rich List put Mr Abramovich's wealth at £9.3bn.

He has owned Chelsea football club since 2003.