LONDON, March 14 (Xinhua) -- Britain has called for an urgent meeting of the UN Security Council to discuss the poisoning of a former spy in Salisbury, the British Foreign Office said here Wednesday.

The action came after Russia failed to respond to a Tuesday midnight deadline set by British Prime Minister Theresa May to explain how an alleged Russian-made nerve agent was used on Sergei Skripal and daughter Yulia.

Russian Foreign Minister Sergei Lavrov said Tuesday that Moscow will ignore May's ultimatum.

Skripal, 66, and Yulia, 33, were reportedly found slumped on a bench in Salisbury city center in Wiltshire on March 4. British police said they remain critically ill in hospital.

The prime minister is set to announce a series of measures against Russia before MPs later Wednesday.

May told MPs on Wednesday that the investigation is under way and vowed to bring perpetrators to justice.

British media have earlier reported that Britain could launch a cyber attack against Russia.

In response, the Russian Embassy in London said Tuesday that talk of cyber attacks is a "serious concern," and urged Britain to carefully consider the consequences of such attacks.

"Not only is Russia groundlessly and provocatively accused of the Salisbury incident, but apparently, plans are being developed in the UK to strike Russia with cyber weapons," the embassy said.

In Russia, Kremlin's spokesman Dmitry Peskov had also denied the country's involvement in the attack.