The crashes of two Russian passenger planes last Tuesday were most likely caused by terrorist attacks, said a senior Russian official Sunday.

Russian Transport Minister Yury Levitin, who is leading a committee to investigate the accidents, told reporters that experts of the country's Federal Security Service (FSB) have found traces of explosives on the wreckage of the two planes, and this has become the main direction for the committee's investigation.

The two crashes are "lessons for everyone of us," said Levitin, adding that the Russian authorities should pay enough attention to the security of air transportation and the parliament should pass special laws over the issue.

In a meeting on the same day, the transport minister also reminded that while emphasizing the security of airliners, the government should not forget the security of trains and buses.

According to Levitin earlier, his committee will draw a primary conclusion within one month over the crashes.

Two Russian passenger jets, Tu-134 and Tu-154, crashed almost simultaneously Tuesday night after taking off from Moscow's Domodedovo Airport, killing all 90 people on board and raising fears of terrorist attacks.

The Tu-134, which was en route from Moscow to the Black Sea resort of Sochi, crashed in Tula region.

Reports from Russia's aviation authorities said the Tu-154 airliner, which carried 46 people on board and crashed in Rostov region, sent hijacking signals before the crash, according to local media report. The airliner was en route from Moscow to Volgograd.

The tragedies came five days ahead of Sunday's presidential election in Chechnya, a breakaway republic of Russia, and separatist rebels there have been blamed for a series of terror activities that have claimed hundreds of lives.

Earlier, an Islamic guerrilla website published a statement in which the Islambouli Brigades group claimed responsibility for the air crashes. The group linked the crashes to events in Chechnya. But so far, the FSB has refused to comment on it.