St Petersburg: Donald Trump decries metro blast as a 'terrible thing'

US President Donald Trump has condemned the Saint Petersburg metro blast which claimed 11 lives, calling it a "terrible thing", as America offered to help Russia in investigating the "act of violence".

"Terrible. Terrible thing. Happening all over the world. Absolutely a terrible thing," he told reporters yesterday during a brief media appearance with visiting Egyptian President Abdel al-Sisi.

White House Press Secretary Sean Spicer said America condemns the act of violence and expresses condolences for the victims.

"The President has been briefed on today's attack on St. Petersburg Metro. The United States condemns this reprehensible attack and act of violence," Spicer told reporters at his daily news conference yesterday.

The United States is prepared to offer assistance to Russia that it may require in investigating this crime, he said.

"Our thoughts and prayers are with the injured and with the Russian people as we extend our deepest condolences to the loved ones who have been killed and injured," he added.

Spicer said that attacks like these on ordinary citizens just going about their lives remind that the world must work as one to combat violence in all forms.

The Investigative Committee, Russia's top criminal investigation body, said it had begun a probe based on the assumption that it was terrorism but added that other possibilities were being considered.

The bomb blast tore through a subway train deep under Russia's second-largest city yesterday, killing 11 people and wounding about 40 in a chaotic scene that left victims sprawled on a smoky platform.

Condemning the blast, US State Department's acting spokesman Mark Toner said, "We extend our deepest condolences to the loved ones of those who were killed, and our thoughts and prayers are with those injured in the attack and with the Russian people".

"Terrorism anywhere threatens the universal values and norms that bind us in common humanity," Senator Ben Cardin, Ranking Member of the Senate Foreign Relations Committee, said.

"It is my hope that the Russian authorities conduct a thorough investigation and that the perpetrators are brought to justice," he said.