One of the two planes that crashed almost simultaneously in the Russian countryside this week fell apart in midair just moments after sending a distress signal, a senior official said Thursday, adding that the plane might have been destroyed by a terrorist explosion.

The presidential envoy who oversees southern Russia for the Kremlin said the evidence, while not conclusive, pointed to a violent destruction of the plane long before it hit the ground, and he declared that the main theory for the cause of both crashes, whose death toll officials now put at 89, "remains terrorism."

The statements made by Vladimir Yakovlev contradicted those of investigators who, the day before, had largely discounted terrorism and cited human or technical error as the likely cause of the crashes. Yakovlev's words proved so sensitive that, later in the day, another official dismissed him as unauthorized to draw conclusions and state television stopped showing the clip of him citing terrorism.

Critics contend that the government is avoiding any use of the word terrorism, at least until after a sensitive election Sunday in the separatist region of Chechnya. President Vladimir Putin, usually quick to blame Chechens when unexplained attacks occur, offered no theory Wednesday and remained out of sight Thursday.

"We have had many tragic cases lately, and the deaths of more than 80 passengers does not add to the reputation of our President Putin," Viktor Ilyukhin, a member of the opposition Communist Party who sits on parliament's security committee, said in an interview. "That is why we are hearing contradictory statements. The authorities do not want to admit it is indeed a terrorist act."

Russian newspapers, which, unlike television, are not directly controlled by the Kremlin, were unusually blunt in criticizing the investigation. "The authorities are failing to see the links between the air crashes and the Chechen presidential election," read a headline in Izvestiya.

Other Russian newspapers, citing unnamed sources, raised questions about a female passenger with a Chechen surname on one of the planes. In response to those reports, the head of the investigation commission, Transportation Minister Igor Levitin, acknowledged late Thursday that authorities were investigating whether she was involved, because no relatives came looking for her body after the crash. "We do not have information that she was a terrorist," Levitin told reporters.

The two passenger jets, one operated by Sibir airline and the other by Volga-Aviaexpress, took off from Moscow's Domodedovo Airport within 40 minutes of each other Tuesday night, heading to different destinations in southern Russia. Both vanished from radar within three minutes of each other, plummeting to the ground about 500 miles apart.

The chief spokesman for the Federal Security Service (FSB), Sergei Ignatchenko, said in an interview Wednesday that the black-box flight recorders from both planes were being analyzed. On Thursday, various officials said the black boxes either were switched off before the crashes or severely damaged by the jets' impacts, and declared that it would be days, if not weeks, before they could be analyzed.

Ignatchenko had predicted the black boxes would prove negligence was the cause. But the FSB was silenced on Thursday. Ignatchenko would not come to the telephone because, an assistant explained, he was not "authorized" to talk.

On Wednesday, Sibir reported it had received a telegram from the government Tuesday night saying its plane's crew had activated a special hijacking alarm.

On Thursday, Levitin said the Sibir plane had sent not a hijacking alarm but a general distress signal just before it disappeared from radar screens, with no voice communication to indicate what the trouble was. But the airline has stuck to its position. "There was a hijacking signal, not an SOS," Sibir spokeswoman Yelena Surgutskaya said by telephone Thursday. "The button exists, but why they pushed this button we don't know."

She rejected an FSB suggestion that faulted the pilots or the airline. She also rejected theories of malfunction. "What happened happened very quickly," she said. "When we look at the distance between the fragments" where they came to rest on the ground, "we can assume there was an explosion."

Yakovlev, the presidential envoy, added that the wreckage was scattered over a large area in suggesting an explosion may have occurred.

Thursday was declared a national day of mourning for the victims.

Workers search wreckage of a passenger plane that crashed Wednesday in southern Russia. Its black box and the one on another plane that crashed were turned off or damaged.