As reported Russia is also suspending all flights to Egypt based on advise from their security services. With UK, US and Russian governments having acted on what they must interpret as credible intelligence, my vote is with a bomb theory, irrespective of all the PPRuNe experts babble.
Indeed, this is actually a major development, and places huge credibility on the bomb theory as he (Putin) is likely to have significant input from MAK.
As Russians are the major tourists to Egypt (followed by the UK as #2) this will really impact the Egyptians.
Updated:
Russia has u-turned on its decision to suspend flying certificates for Boeing 737s, in a further hint that it no longer believes the fault for the Sinai plane crash was mechanical.
Think they mean Airbus...