Egypt plane crash: airport employees reportedly detained as Russia says jet was bombed

"Seventeen people are being held, two of them are suspected of helping whoever planted the bomb on the plane at Sharm el-Sheikh airport," one of the officials said.

Until Tuesday, Russia had played down assertions from western countries that the crash, in which 224 people were killed, was a terrorist incident, saying it was important to let the official investigation run its course.

But in a Kremlin meeting on Monday night, three days after Islamist gunmen and bombers killed 129 people in Paris , Alexander Bortnikov, the head of Russia's FSB security service, told a meeting chaired by President Vladimir Putin that traces of foreign-made explosive had been found on fragments of the downed plane and on passengers' personal belongings. The plane was returning holidaymakers to St Petersburg from the resort town of Sharm el-Sheikh.

"According to an analysis by our specialists, a homemade bomb containing up to 1 kilogramme of TNT detonated during the flight, causing the plane to break up in mid-air, which explains why parts of the fuselage were spread over such a large distance," said Bortnikov. "We can unequivocally say it was a terrorist act," Bortnikov said in footage that was not released until Tuesday morning.

Putin responded by saying the incident was one of the bloodiest acts in modern Russian history and ordered the Russian air force to intensify its airstrikes in Syria in response. "It [the air campaign] must be intensified in such a way that the criminals understand that retribution is inevitable," he said.

Ordering the country's secret service to search for those responsible for blowing up the plane, he said the effort to bring them to justice should be exhaustive. "We will search for them everywhere wherever they are hiding. We will find them anywhere on the planet and punish them," Putin said.

Interfax, the Russian news agency, reported that the FSB was offering a $50m (£33m) reward for information that led to the capture of those who planned the attack.

Last week, Britain's foreign secretary said there was a high probability that a bomb planted by a supporter of Islamic State brought down the Russian aircraft. Philip Hammond told CNN: "It may have been an individual who was inspired by Isis who was self-radicalised by looking at Isis propaganda and was acting in the name of Isis without necessarily being directed."

US officials also suspect a device planted on Metrojet flight 9268 exploded shortly after the Airbus A321 took off from Sharm el-Sheikh. An Isis affiliate has claimed responsibility for the attack.

Source: The Guardian Photograph: Maxim Grigoryev/AFP/Getty Images