A police officer stands at a cordon around the bench where former Russian intelligence agent Sergei Skripal and his daughter Yulia were found after they were poisoned on March 14, 2018. Photo: Reuters / Henry Nicholls.

Prime Minister Theresa May was due to announce on Wednesday what Britain would do against Russia after a midnight deadline she set expired without an explanation from Moscow about how a Soviet-era nerve toxin was used to attack a Russian ex-spy.

Sky News reported that May would expel a significant number of Russian diplomats. Her Downing Street office declined to comment and said she would outline the British response in a statement to parliament, expected around 1230 GMT (8.30 a.m. ET).

The United States, European Union and NATO voiced support for Britain after May said it was “highly likely” that Russia was behind the poisoning of Sergei Skripal and his daughter with Novichok, a nerve agent developed by the Soviet military.

Russia, which denied any involvement, said it was not responding to May’s ultimatum until it received samples of the nerve agent, in effect challenging Britain to show what sanctions it would impose against Russian interests.

“Moscow had nothing to do with what happened in Britain. It will not accept any totally unfounded accusations directed against it and will also not accept the language of ultimatums,” Kremlin spokesman Dmitry Peskov told reporters on Wednesday.

He said Russia remained open to cooperating with Britain in investigating the poisoning, blaming the British authorities for refusing to share information.

Russia’s Interfax news agency reported the Russian embassy in London planned to ask for consular access to Yulia Skripal, Sergei’s daughter.

Russian Foreign Minister Sergei Lavrov said no progress had been made toward resolving the standoff, describing claims of Russian involvement in the attack as neither robust nor serious.

May chaired a meeting of the National Security Council at her Downing Street office on Wednesday morning and was expected to make a formal statement to parliament on the Skripal attack after her weekly question-and-answer session with lawmakers.

Trump support for UK

The Foreign Office said Britain had called for an urgent meeting of the United Nations Security Council to update members on the attack. Russia is also a member of the council.

The European Union Council’s president, Donald Tusk, said he was ready to put the attack on the Skripals on the agenda for a summit next week.

London could call on Western allies for a coordinated response, freeze the assets of Russian business leaders and officials, limit their access to London’s financial center, expel diplomats and even launch targeted cyber attacks.

It may also cut back participation in the soccer World Cup, which Russia is hosting in June and July.

Russia is due to hold a presidential election on Sunday in which Vladimir Putin, himself a former KGB spy, is expected to coast to a fourth term in the Kremlin. He was first installed as Kremlin chief by Boris Yeltsin on the last day of 1999.

US President Donald Trump told May by telephone Russia “must provide unambiguous answers regarding how this chemical weapon, developed in Russia, came to be used in the United Kingdom,” the White House said.

The White House said Trump and May “agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms.”

A British readout of the conversation said, “President Trump said the US was with the UK all the way.”

Skripal, 66, and his daughter Yulia, 33, were found slumped unconscious on a bench outside a shopping center in the genteel southern English city of Salisbury on March 4. They have been in a critical condition in hospital ever since.

British scientists identified the poison as a military-grade nerve agent from a group of chemicals known as Novichok, first developed in the Soviet Union in the 1970s and 1980s.

May said either the Russian state had poisoned Skripal, a former Russian military intelligence officer, or Russia had somehow lost control of its chemical weapons. Putin said last year that it had destroyed its last stockpiles of such weapons.