ABCNews.com(LONDON) — The UK has given 23 Russian diplomats identified as intelligence officers one week to leave the UK, the biggest expulsion in decades in retaliation for the poisoning of a former Russian double agent in early March.

Prime Minister Theresa May also said that the UK was looking to implement new powers to its sanctions bill, styled on the Magnitsky Act in the United States, which allowed America to freeze assets and withhold visas of foreign officials thought to be involved in corruption and human rights.

In addition, Russian state assets will be frozen where they threaten UK nationals or residents, and all planned high-level contact between the UK and Russia is to be suspended, including an invite for Russian Foreign Minister Sergey Lavrov to come to the country.

British officials and the royal family will also not attend the 2018 World Cup in Russia.

A midnight Tuesday deadline set by May for Russia to provide a “credible” explanation for how Sergey Skripal was poisoned by a Soviet-era nerve agent in Salisbury passed with no response from the Kremlin.

Skripal’s daughter, Yulia, was also poisoned in the incident. Both were in critical condition.

May warned Russian President Vladimir Putin that if the Kremlin did not cooperate, London would interpret the incident as an “unlawful use of force” by the Russian state against the UK.

Lavrov, speaking ahead of the Prime Minister’s statement, said that the expulsion of diplomats from the UK over the Salisbury incident was “unacceptable” and a “provocation”.

The expulsion is the biggest removal of Russian staff since more than 100 Soviet diplomats and spies were booted by former Prime Minister Edward Heath’s government in 1971, plunging UK-Soviet relations to an historic low.

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