President Boris Yeltsin's envoy to Chechnya has said Russia will investigate reports of air raids in the breakaway region which Chechens have blamed on Moscow.


A spokesman for Chechen rebel leader Dzhokhar Dudayev has accused Russian planes of attacking two villages in southern Chechnya on Saturday, killing 17 people and injuring 23 others.


But Moscow envoy Oleg Lobov, quoted by Itar-Tass on Tuesday, recalled an order by Yeltsin banning such air raids which killed a large number of civilians in the capital Grozny in the early days of the Russian intervention last December.


The Russian air force has denied renewing military missions.


"Bombing attacks are banned. There is a presidential order on this," Lobov was quoted as telling reporters after arriving in Grozny on Monday.


Lobov said the weekend air raids were reported to have occurred in territory held by "illegal armed groups" -- the phrase used for rebel fighters -- so it would be hard to establish what happened.


"The prosecutor's office will have to carry out the investigation," Lobov said, adding that both Russian forces and Chechens would have to assist in such an investigation.


Violence has been steadily mounting in Chechnya despite an official cease-fire, with Russians and rebels accusing each other of stepping up military activity.


Russian forces shelled the southwest Chechen village of Orekhovo on Tuesday after an ultimatum ran out for rebel fighters said to be hiding there.


Reuters cameraman Igor Shatalov, who was filming nearby, heard artillery shells being launched for five minutes from Russian positions around Orekhovo and saw smoke rising from the village 35 kilometers southwest of Grozny.


Women who had fled the village before the ultimatum ran out Monday said only two civilians had stayed behind.


Russia has promised to withdraw its forces gradually from the north Caucasus region in return for rebel disarmament, but the process has proved complex.


A cease-fire, agreed after thousands of people had been killed in six months of heavy fighting, has come under severe strain since Russia's military commander Lieutenant General Anatoly Romanov was critically injured in a remote-control bomb attack on Oct. 6 which Russia blames on the rebels.


"The situation is unstable. Every outcome is possible, including the most serious one," Interfax quoted Lieutenant General Anatoly Shkirko, Romanov's successor, as telling journalists in Grozny on Tuesday.


Shkirko said an investigation was going on into a separate air raid earlier this month on the village of Roshni-Chu, southwest of Grozny, which the Chechens say killed 28 people.


"We will have to work out in detail what happened. Military prosecutors are leading the investigation," Shkirko told Itar-Tass. The Russians have denied responsibility for the attack.


On Tuesday, Itar-Tass quoted the federal troops' press service in Chechnya as saying two of its servicemen had been killed in the previous 24 hours in attacks by Dudayev's forces.