GENEVA – Britain told the U.N. Human Rights Council on Wednesday that the use of a military grade nerve agent used in an attempt to kill a former Russian spy was a flagrant breach of international law and should serve as a warning to the international community.

“The council and the United Nations General Assembly have decried Russia’s violations of international law with alarming regularity. Its reckless behavior is an affront to all this body stands for,” British Ambassador Julian Braithwaite said.

Britain was braced for a showdown with Russia on Wednesday after a midnight deadline set by Prime Minister Theresa May expired without an explanation from Moscow about how a Soviet-era nerve toxin was used to strike down a former Russian double agent.

Prime Minister Theresa May has said it was “highly likely” Russia was behind the poisoning of Sergei Skripal and his daughter with 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.

Russia’s representative at U.N. Human Rights Council did not refer to the incident in his speech to the Geneva forum, but focused on alleged human rights violations against Afro-Americans in the United States.

Braithwaite listed a string of complaints against Russia, echoed by others including the United States.

“From Ukraine to Syria, and now the United Kingdom, Russia continues to be an irresponsible force of instability in the world, acting with open disregard for the sovereignty of other states and the lives of those living within their borders,” said Jason Mack, a first secretary at the U.S. mission in Geneva.

In a speech last week, Zeid Ra’ad al-Hussein, U.N. High Commissioner for Human Rights, denounced what he called “an orchestrated and coordinated campaign of violence and threats” against a leading Russian human rights group, Memorial Human Rights Centre in Chechnya, Ingushetia and Dagestan.

Zeid, referring to the presidential elections on March 18, also called on Moscow to ensure that people are allowed to peacefully assemble and that freedom of expression is protected.