Russia has said for the first time that a bomb brought down a Russian passenger jet over Egypt last month and promised to hunt down those responsible.

Russia had played down assertions from western countries that the crash, in which 224 people were killed on 31 October, was a terrorist incident, saying it was important to let the official investigation run its course.              

But last night, 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.              

"According to an analysis by our specialists, a home-made bomb containing up to 1kg 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 Mr Bortnikov.              

"We can unequivocally say it was a terrorist act," Mr Bortnikov said in footage that was not released until this morning.              

Mr 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 air strikes in Syria in response.              

"It [our campaign] must be intensified in such a way that the criminals understand that retribution is inevitable," said Mr Putin.              

Ordering the country's secret service to hunt down 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," Mr Putin said.

Meanwhile, Egyptian authorities have detained two employees of Sharm el-Sheikh airport in connection with the crash. 

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