Moscow, Mar 31 (IANS): A Russian plane was searched by the British authorities at London's Heathrow airport without citing any reasons, Russian officials said.

The British authorities conducted the search on the Aeroflot plane on Friday after compelling the crew to leave the aircraft, the officials were cited as saying by TASS news agency.

"The British side provided no grounds for a plane search. It was decided that after the British side finishes the search, the plane will be additionally examined by the crew and the company's office employees. The British side compelled the crew to leave the plane during the search," an Aeroflot official told the news agency.

The Russian Embassy in Britain said in a statement: "Border Force and Customs officers have searched the aircraft that was conducting the Aeroflot flights 2582/2583, Moscow --London-- Moscow. This kind of event is extraordinary."

Russia's relations with the UK strained following the alleged poisoning of former Russian double spy Sergei Skripal and his daughter Yulia on British soil. Skripal had been convicted in Russia of spying for the UK and was later swapped for Russian intelligence officers.

On March 4, Skripal and his daughter were found unconscious on a bench near a shopping centre in Salisbury. Police said they had allegedly been exposed to a nerve agent. Skripal was still in critical condition in hospital while his daughter was out of danger.

Britain blamed Russia for the poisoning attack but Moscow denied any responsibility for it. The UK then expelled 23 Russian diplomats and announced other restrictive measures against Moscow.

In response, Moscow expelled a similar number of British diplomats from Russia and ordered the closing of the British Consulate-General in St. Petersburg. It also ordered the shutting of the British Council's offices in Russia.

So far, some 150 Russians have been expelled by mainly Western countries in solidarity with the UK. Meanwhile, Russia on Friday called in a string of foreign ambassadors with news that their own countries' measures were being matched.