The weekly "Frankfurter Allgemeine Sonntagszeitung" (FAS) reported in its Sunday edition that the German government believes the Russian Metrojet airliner was bombed by the "Islamic State" (IS) terrorist group.

"All available information points to this conclusion," a senior German security official told the paper, adding that the aircraft's sudden drop in altitude, without any irregularities having been recorded in the cockpit, make a bomb "very plausible."

'A noise was heard'

At a press conference on Saturday, Egyptian authorities said investigators were still unable to determine the cause of the crash.

"Initial observations ... do not allow for identifying the origin of the in-flight break-up," said investigation committee leader Ayman al-Muqaddam.

He added, however, that "a noise was heard in the last second of the recording by the cockpit voice recorder" and "a spectral analysis will be done to determine [its] origin."

Russia suspends flights

The Russian passenger jet crashed last Saturday, 23 minutes after taking off from the Sinai resort of Sharm el-Sheikh. All 224 people on board the St. Petersburg-bound flight were killed - most of whom were Russian holidaymakers.

Sinai has been the scene of an Islamist insurgency in Egypt for nearly two years, leaving scores of people dead, including Egyptian soldiers and police officers.

The United States and United Kingdom have already suggested that a bomb was the likely cause of the crash. Russia and Egypt, however, have said they will wait for a full investigation before appointing blame. Russian President Vladimir Putin has now suspended Russian flights to Egypt.

US reports IS 'celebrations'

US broadcaster NBC said on Friday that "Islamic State" (IS) terrorists had been recorded bragging about the recent crash.

Citing unnamed US officials, NBC said they were told that the "chatter" included details of how the plane went down.

"They were clearly celebrating," one official told NBC Nightly News.

Separately, CNN showed a video released by IS that purports to show leaders in Aleppo, congratulating their cohorts in Sinai on the tragedy.

ksb/sms (AP, Reuters, dpa)