MOSCOW, July 16 -- Two Chinese men were confirmed dead after a metro train derailed in Moscow at the morning rush hour Tuesday, the Chinese embassy said early Wednesday.

The latest death toll was based on an on-the-spot verification by consular officials with the Chinese embassy, as of 1:25 a.m. local time (2125 GMT Tuesday).

The Chinese embassy had contacted with the victims' companies that dispatched the two Chinese to Moscow, and a working group of the embassy was in contact with relevant Russian departments to closely follow the developments.

The Chinese nationals, who were to be further identified, were killed when three carriages derailed during an emergency braking in an underground tunnel in western Moscow between Slavyanski Bulvar and Park Pobedy stations.

Russian Health Minister Veronika Skvortsova said the incident has claimed at least 21 lives and injured some 200 more.

Moscow Mayor Sergei Sobyanin declared Wednesday as a day of mourning for the victims, and pledged to bring those responsible to account.

Russian President Vladimir Putin, who is currently in Brazil, offered "deep condolences to the relatives and loved ones of those killed and wishes a swift recovery for those injured in the crash," Kremlin spokesman Dmitry Peskov told reporters.

The president has also instructed Russia's Investigative Committee (IC) to open criminal cases over the incident. IC spokesman Vladimir Markin has ruled out the possibility of a terror attack, saying "it is a technical incident."

Tuesday's incident could become the worst technical disaster in the history of Moscow metro, which was established in 1935. On June 5, 2013, the Moscow metro was suspended twice in a day due to technical failures, injuring dozens of people.