A Sibir Airlines Tupolev 154, similar to one of the crashed aircraft, is seen in this 2004 photo. (Koos van der Heijden/View Full Size)

As many as 94 people are feared killed.

Both planes took off from the same Moscow airport within minutes of each other late Tuesday and were bound for southwestern Russian cities.

The first plane disappeared from radar at 10:56 p.m. (0756 GMT), the news agency said.

The second plane, a Tupolev 154, dropped off the radar shortly afterwards.

That plane issued a signal indicating a hijacking or seizure before going missing, the Interfax news agency quoted an unidentified government source as saying on Wednesday.

CNN has no independent confirmation on whether the hijacking alarm was activated.

Russian officials have reportedly found the crash sites of both planes.

Witnesses reported seeing the first plane explode before it crashed, Interfax reported.

A ministry spokeswoman said the wreckage was found ablaze in the Tula region, about 160 kilometers (100 miles) south of Moscow.

The government-run news agency Ria Novosti reported that the plane's wreckage was in two separate locations.

Search and rescue teams were at the site searching for possible survivors, but the ministry said none of the 34 passengers and eight-member crew are believed to have survived.

The second plane, carrying with between 46 and 52 people on board, was about 100 miles (160 kilometers) from Rostov-on-Don when it dropped off radar screens.

Officials did not say whether any survivors were found from the second wreckage.

Immediate investigation

Russian President Vladimir Putin has ordered security services to launch an immediate investigation, news agencies reported early Wednesday.

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The first plane, a Tupolev-134, had taken off from Moscow's Domodedovo Airport and was en route to Volgograd, in southern Russia.

The second plane disappeared from radar at 10:59 p.m. after having taken off from the same airport en route to Sochi, a tourist resort on the Black Sea in southern Russia, the ministry spokeswoman reported.

The Tupolev-154 is a standard medium-range airliner on domestic flights in Russia, according to aviation websites.

Russian authorities offered no explanations for the crashes but said they had increased security at airports following an explosion at a Moscow bus station earlier Tuesday, which injured three people.

"If this were just one, you would look toward some sort of aircraft issue," Peter Goelz, a former managing director of the U.S. National Transportation Safety Board, told CNN.

"But with two of them going down so close together, it's awfully ominous."

The incidents also took place just days before a regional election in the rebellious southern territory of Chechnya, where Russian troops have battled separatist guerrillas for five years.

Chechen separatists have been blamed for numerous bombings and other attacks in Russia in recent years, including the seizure of hundreds of hostages at a Moscow theater that ended with more than 100 hostages dead.