Egyptian and Russian officials countered U.S. and U.K. claims that a bomb connected with the Islamic State group brought down a Russian plane in Egypt's Sinai peninsula Saturday. Above, the remains of the plane are inspected by military investigators, Nov. 1, 2015. Reuters/Mohamed Abd El Ghany

Claims by the United States and United Kingdom that a bomb may have brought down the Russian plane that crashed in Egypt's Sinai Peninsula Saturday, killing all 224 aboard, were pure "speculation," the Kremlin said Thursday. Egypt, too, warned that investigations had turned up "no evidence or data" yet to confirm the idea.

"We cannot be certain that the Russian airliner was brought down by a terrorist bomb, but it looks increasingly likely that that was the case," U.K. Prime Minister David Cameron said Thursday. British Foreign Secretary Philip Hammond said that there was a "significant possibility" that the Islamic State group, which has a Sinai-based affiliate known as Wilayat Sinai (Sinai Province), was responsible.

One United States official also told CNN Wednesday that "there is a definite feeling it was an explosive device planted in luggage or somewhere on the plane.” That early assessment was based on the most recent U.S. intelligence, although a formal conclusion had yet to be drawn. Some of that intelligence was based on messages sent within the Islamic State group, and not on the group's claim Saturday shortly after the crash that it had taken down the plane.

But Dmitry Peskov, spokesman for the Kremlin, said it was too soon to draw such conclusions, the BBC reported. "Theories about what happened and the causes of the incident can only be pronounced by the investigation," he said. "Any kind of similar assumptions like this are based on information that has not been checked or are speculation," he added.

Egyptian authorities offered similar warnings.

"We do not want to rush into conclusions," Egyptian President Abdel Fattah el-Sisi said. He had previously described the idea that militants belonging to the Islamic State group brought down the plane as "propaganda." He said Tuesday, "This is one way to damage the stability and security of Egypt and the image of Egypt. Believe me, the situation in Sinai -- especially in this limited area -- is under our full control."

Britain stopped flights Thursday both to and from Sharm el-Sheikh, the resort town at the southern tip of Sinai from which Saturday's plane departed. But the country was expected to start flying home British citizens who remained in the town Friday.