He was speaking after US and UK officials said intelligence suggested the plane may have been bombed.
Militants linked to Islamic State (IS) have claimed that they brought it down.
The Metrojet Airbus 321, bound for St Petersburg, crashed in Egypt`s Sinai desert just 23 minutes after take-off from Sharm el-Sheikh on Saturday.
Most of those on board the plane were Russian.
On Thursday, the UK suspended flights to and from Sharm el-Sheikh, leaving thousands of Britons stranded at the resort.
UK Foreign Secretary Philip Hammond said the government had looked at all the information available, including the claim by IS, and concluded that there was a "significant possibility" the plane had been brought down.
But Egyptian President Abdul Fattah al-Sisi, who is on a visit to the UK, told the BBC: "We do not want to rush into conclusions. We all share the same concerns. We want to know the reasons behind it.
"The investigation will be disclosed with all transparency, we have nothing to hide."
Mr Sisi, who is due to meet UK Prime Minister David Cameron, had previously dismissed the IS claim as propaganda.