A plane can disappear from radar when it gets too close to the ground to reflect radar signals.

John Cox, a former airline pilot and now a US-based safety consultant, said the disappearance could also indicate that the jet's transponder lost power.

"That says potential of engine failure or a technical problem," Cox told The Associated Press.

President Vladimir Putin put off a planned trip to Sochi to monitor the investigation. Putin was to meet Monday with Palestinian leader Mahmoud Abbas at the Black Sea resort, where the president has an official residence.

Instead, Abbas will meet with Putin in Moscow in the latter part of Monday, Kremlin spokesman Dmitry Peskov told Russian news agencies.

The An-148 was developed by Ukraine's Antonov company in the early 2000s and manufactured in both Ukraine and Russia.

Shabby equipment and poor supervision plagued Russian civil aviation for years after the 1991 collapse of the Soviet Union, but its safety record has improved in recent years.

The last large-scale crash in Russia occurred on Dec 25, 2016, when a Tu-154 operated by the Russian Defense Ministry on its way to Syria crashed into the Black Sea minutes after takeoff from Sochi. All 92 people on board were killed.

In March 2016, a Boeing 737-800 flown by FlyDubai crashed while landing at Rostov-on-Don, killing all 62 people aboard.

An onboard bomb destroyed a Russian Metrojet airliner in October 2015 soon after it took off from Egypt's Sharm al-Sheikh resort. The bombing killed 224 people.