LONDON, March 13 (Xinhua) -- U.S. President Donald Trump has told British Prime Minister Theresa May that his administration backs Britain "all the way" over the ex-Russian-spy poisoning case, a Downing Street spokesperson said Tuesday.

May had concluded that it was "highly likely" Russia was to blame for the poisoning of ex-spy Sergei Skripal and his daughter in the southern English town of Salisbury.

The spokesperson said in a statement that May spoke to Trump earlier Tuesday afternoon to update him on the investigation into the Salisbury incident and set out the conclusion reached by the British government that it was highly likely that Russia was responsible for the attack.

"President Trump said the U.S. was with the UK all the way, agreeing that the Russian government must provide unambiguous answers as to how this nerve agent came to be used," the spokesperson said.

The White House also released a statement earlier Tuesday, saying that Trump stated the United States stands in solidarity with "its closest ally" and is ready to provide any assistance the United Kingdom requests for its investigation.

"President Trump agreed with Prime Minister May that the Government of the Russian Federation must provide unambiguous answers regarding how this chemical weapon, developed in Russia, came to be used in the United Kingdom.

"The two leaders agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms," said the White House statement.

A Downing Street spokesman said May has also called French President Emmanuel Macron and German Chancellor Angela Merkel earlier to update them of the investigation, both Macron and Merkel have condemned the attack and offered their solidarity with Britain.

Former Russian intelligence officer Sergei Skripal and his 33-year-old daughter Yulia, a Russian citizen, were found unconscious on a bench at a shopping center in the district of Salisbury, England, on March 5. They remain in critical condition in hospital, according to British media reports.

Earlier on Tuesday, Russian Foreign Minister Sergei Lavrov said that Russia, while denying any involvement in the poisoning case, was ready to cooperate with Britain in the investigation of the incident in accordance with international law,

"Russia is innocent and Russia is ready to cooperate in accordance with the Chemical Weapons Convention if the United Kingdom condescends to honoring its international legal obligations related to the mentioned document," Lavrov told a press conference in Moscow.