MOSCOW – A Russian passenger plane crashed and another was reported missing last night in what authorities feared might be a coordinated terrorist attack.

The Russian news agency Interfax reported that a hijacking signal was activated on the second plane before it went missing.

A TU-134 with 43 passengers and crew flying from Moscow to Volgograd crashed near Tula, about 90 miles south of Moscow. Contact with the plane was lost just before 11 p.m. Moscow time and witnesses reported seeing an explosion on board before it went down. Emergency workers on the scene had no word of survivors.

Rescue teams found the jet’s tail near the village of Buchalki,Interfax reported.There was no information about survivors, but none were expected to be found.

Just three minutes later, air traffic controllers lost contact with another passenger plane – a TU-154 with 46 people on board – flying from Moscow to the Black Sea resort of Sochi, where President Putin is vacationing. Contact was lost with the plane as it was flying near the southern city of Rostov-on-Don, about 600 miles south of Moscow. Early reports by Russian news agencies quoted emergency officials saying that the second plane had also crashed. Those reports remained unconfirmed, but news agencies reported that emergency workers had spotted a fire in the region where the second plane went missing.

Both planes took off from Moscow’s Domodedovo airport.

Authorities tightened security at all of Russia’s airports following the incidents.Mr.Putin ordered the Federal Security Service, or FSB, the former KGB, to investigate. The FSB is not normally involved in investigating such accidents unless the circumstances are deemed suspicious.

When told of the initial report of two crashes, Russia’s U.N. ambassador, Andrei Denisov,said: “Now we have to see if there’s terrorism.” In Washington, a senior State Department official said: “We are obviously concerned by the news. We’re following developments closely and trying to determine the facts.”

The crash comes only days before Sunday’s president election in the breakaway southern republic of Chechnya, where Russian forces are fighting a brutal campaign against separatist rebels.The rebels have claimed responsibility for a series of deadly explosions and suicide bombings in recent years that have claimed the lives of hundreds.

The vote follows the assassination of Chechnya’s pro-Moscow president, Akhmad Kadyrov, in a bomb attack at a stadium in the Chechen capital, Grozny, on May 9. Rebel groups have promised to disrupt Sunday’s vote, which they say is a sham to install the pro-Kremlin candidate, Alu Alkhanov.

This week has seen some of the deadliest fighting in Grozny in more than a year. Russian artillery strikes killed 12 rebels yesterday outside Grozny in retaliation for a brazen raid in the capital on the weekend that killed at least 30 people. In a well-orchestrated attack, coordinated rebel units simultaneously attacked state targets, including checkpoints, police, and polling stations throughout Grozny around 8 p.m. Saturday before pulling out after midnight.

The attack was strikingly similar to an assault by terrorists two months ago on police facilities in Ingushetia, adjacent to Chechnya, that left 90 people dead and deeply embarrassed the Russian military, leading to the dismissal of a number of top defense officials.

Following Saturday’s attack, a rebel commander was quoted by Chechen Web site Kavkaz Center as warning that further actions, including attacks outside Chechnya, were being planned.

“Our actions will not be confined within the territory of Ichkeria alone,” said the unidentified rebel leader, using the rebels’ name for Chechnya. “Today the entire North Caucasus and all of Russia is a war zone.We will be carrying out attacks wherever we deem necessary.”

The head of public relations for the FSB, Sergei Ignatchenko, said earlier this month that intelligence suggested that foreign terrorist groups had recently sent money to Chechen rebels to be used to disrupt the elections.