For the first time, Russian security chiefs have admitted a bomb did bring down the passenger plane that crashed over the Sinai Peninsula in Egypt last month. 

Russian airliner A321 crashed en route from Egypt to St Petersburg, Russia, but crashed in the Sinai desert on October 31, killing all 224 people on board. British Prime Minister David Cameron and other western leaders suspected a terror attack and said intelligence suggested a bomb on board caused the crash. However the Kremlin has refused to admit this until now.

"One can unequivocally say that it was a terrorist act," said Alexander Bortnikov, the head of Russia's FSB security service, in a meeting chaired by President Vladimir Putin today.

"Traces of foreign explosives" were found among the debris of Airbus A321, Bortnikov told Putin. 

The Russian President promised to "find and punish" those responsible for the attack. 

"We'll look for them everywhere, wherever they are hiding," he said. "We'll find them in any corner of the planet and punish them."

An ISIS affiliate has claimed responsibility for the attack which, experts suggest, is in retaliation for Russia's heavy bombardment of Syria, where ISIS control large swathes of land. However in response to the attack, Putin said that the airstrikes must not only continue but must be intensified "so that the criminals understand that retribution is inevitable."

Most of the 224 dead were Russians flying home from the Egyptian tourist destination of Sharm el-Sheikh. 

Additional reporting from Reuters.