Russian officials are now convinced that a bomb caused the mid-air explosion of Metrojet Flight 9268, killing all 224 people on board, US intelligence sources have revealed.

Ahead of a formal announcement, Moscow appeared to have accepted the assertions made by British and American officials that terrorists, possibly with ties to the Islamic State (ISIS), were responsible for the fiery crash of the Russian airliner that took off from the Egyptian resort city of Sharm al-Sheikh bound for St. Petersburg, Russia on Oct. 31, the sources said.

Communications intercepted by U.S. intelligence agencies indicated that Moscow now believes that the crash could be linked to ISIS, the Daily Express said.

The terrorism angle was again underscored by British Foreign Secretary Philip Hammond on Monday, saying "it's more likely than not that it was an explosive device on the aircraft" and "there's going to be a high probability" that ISIS was involved.

However, Hammond said an official announcement of the cause of the crash can only be made after an analysis of the plane wreckage has been completed.

Russia vented its fury on the battlefield, announcing that its air force has struck 448 enemy targets in Syria in three straight days of airstrikes.

Meanwhile, a controversial Russian commentator appeared to accuse the United States of complicity in the disaster.

Speaking on the popular Russian TV news programme Vesti Nedeli (News of the Week), Dmitry Kiselyov said: "If it is really so [that ISIS was to blame for the downing of the Russian plane], a question pops up: why against Russia who has been fighting against ISIS for less than 40 days?

"Americans, as the head of their coalition, have been bombing for two years and have completed over 60,000 flights [but] there has been nothing against them. No single terrorist attack," the Daily Mail reported, quoting an English transcription of the show.

Kiselyov went on to say: "It is known that the American military easily find a common language with terrorists when it comes to their safety. They either buy or arrange some sort of swap. Like 'we shut our eyes to something, and you don't touch us.'

"This has been practised for years with Taliban in Afghanistan. Why not repeat the experience with the ISIS, to everyone's pleasure, through the mediation of Qatar?"

The pro-Kremlin pundit said, "Dividing terrorists into good and bad ones is another common practice for the West. If it's against Russia, it's a good terrorist and even a democrat."

He then zeroed in on the fact that the Obama administration is strongly opposed to Russia's support of the government of Syrian President Bashar al-Assad. Kiselyov recalled that on Oct. 9, U.S. Defence Secretary Ashton Carter "predicted that Russia will have terrorist attacks and human losses in the near future."

Kiselyov, 61, has been described by Bloomberg as "the public face of Putin's propaganda machine and one of the regime's top functionaries."

In December 2013, he was appointed as head of the new official Russian government-owned international news agency Rossiya Segodnya (Russia Today).

He also serves as deputy director of Russian state TV holding company VGTRK.

Kiselyov is well known in the West for his controversial comments. He gained extra notoriety when he said last year during the Crimean crisis that Russia is "the only country in the world capable of turning the USA into radioactive dust."