Russian investigators scoured the gutted remains of a trolley bus destroyed by a suicide bomber on Monday and said a former paramedic who converted to Islam and joined a terrorist underground was responsible for another horrific attack at a train station just hours before.

Fourteen people were killed in the bus blast in Volgograd, while 17 died in the explosion at the city’s train hub.

Officials said little about the bus bomber but identified the earlier attacker as Pavel Pechyonkin, who left a note to his mother and vanished from his home more than a year ago to join militants in the Dagestan region.

“I have come here only to make Allah happy, to earn heaven,” he said in a video posted on YouTube earlier this year after his parents pleaded with him in their own video to renounce terror.

“Why should we follow those Christian commandments, when Allah, may he be glorified, urges us to fight those kafirs [infidels]?” he added. “Why shouldn’t we leave their children orphans?”

Russian investigators believe Pechyonkin exploded the equivalent of 22 pounds of TNT at the Volgograd train station on Sunday.

A second suicide bomber, using explosives of the same type and amount, struck the trolley bus in the heart of the city still known to many Russians as Stalingrad, the site of a turning-point battle of World War II.

In addition to the dead, the bombings wounded 104 people, including 58 who remained hospitalized late Monday.

The attacks, coming a month before the Winter Olympics in Sochi, about 400 miles from Volgograd, are a major embarrassment for President Vladimir Putin. The Kremlin leader is expected to order armed raids on militant targets in Dagestan — a center of terror activity and briefly home to the Boston Marathon bombers.

The White House said Monday that the United States was offering “full support” and “closer cooperation” with Russia on security preparations for the Olympics

— despite frigid relations between Washington and Moscow.

Australia became the first nation to publicly talk about backing out of Sochi. “We don’t want to lightly prevent our athletes participating in any event for which they’ve trained for years,” Foreign Minister Julie Bishop said.

“But their safety and the safety of their families and other spectators is of utmost concern.”

With Times of London and Post Wire Services