The British embassy in Russia is pictured on March 15, 2018. (Xinhua/Wu Zhuang)

MOSCOW, March 31 (Xinhua) -- More than 50 staff members of Britain's diplomatic missions in Russia have to leave as tensions between Russia and the West have sharply escalated over the death of an ex-spy, a local report said Saturday.

The Russian Foreign Ministry announced Friday that Britain must downsize its personnel in diplomatic missions in Russia within a month to the same level as Russia has in Britain, without disclosing how many people will be expelled.

"Russia offered parity. Britain has over 50 people more (than the Russian staff in Britain)," Interfax news agency reported, citing Russian Foreign Ministry spokesperson Maria Zakharova.

Former Russian intelligence officer Sergei Skripal and his daughter Yulia were reportedly exposed to a nerve agent and found unconscious on a bench at a shopping center in the British city of Salisbury on March 4.

Britain accused the Kremlin of masterminding the attempted murder of the two Skripals by employing a Soviet-era, military-grade nerve agent Novichok. The Russian government denied any role in the case.

On March 14, Britain announced the expulsion of 23 Russian diplomats and Russia expelled an equal number of British diplomats three days later.

In a show of solidarity with Britain, many European countries and the United States announced the expulsion of around 150 Russian diplomats.

The Russian Foreign Ministry on Friday informed ambassadors of 23 countries of its decision to expel employees of their diplomatic missions in Russia in a tit-for-tat response to actions by their countries against Moscow.