Both the planes went off the radar screens on Tuesday within a minute of each other and an air traffic control source said the possibility of a terrorist attack could not be ruled out.

A Russian emergency ministry spokeswoman said a Tupelov Tu-134 aircraft with 34 passengers and eight crew on board was en route from Moscow to the southern city of Volgograd when it disappeared off radar screens at 1900 GMT.

Its tail was later found near the village of Buchalki in the Tula region some 180 km south of Moscow, spokeswoman Marina Ryklina said.

Explosion

Local emergency ministry officials cited witness reports of an explosion aboard before the airplane went down.

A minute before that crash, a Tu-154 airplane with 46 people on board went missing near the southern city of Rostov-on-Don during a flight from Moscow to the Black Sea resort of Sochi.

Both planes left from Moscow's Domodedovo airport and dropped off radar screens within a minute of each other.

Russian President Vladimir Putin ordered the security service to investigate both incidents without delay, the Kremlin press service said.

The Interstate Aviation Committee, formed by 12 former Soviet republics, would also investigate the incident.

Unnamed sources said security has been boosted at all Russian airports.