Four Russian soldiers have been killed in an attack on their base near Vedeno in the south of Chechnya.
A Russian general says it is too early to call Chechnya stable
Three other soldiers, including a senior officer, were wounded before the attackers fled.
Russian federal forces are searching for the group - believed to be separatist rebels.
A Russian army general has insisted that Chechnya is becoming calmer, but admitted it was still too early to describe the situation there as stable.
The BBC's James Rodgers in Moscow says that while the fighting is far less intense than it has been at times during the 11-year conflict, Chechnya remains dangerous and lawless.
On Tuesday the human rights group Amnesty International accused Russian troops and Chechen forces allied to them of serious abuse.
Its annual report said abductions, torture, killings and arbitrary detentions were continuing in Chechnya.
Amnesty said those responsible went unpunished, and pointed out that there had been just two convictions for serious human rights violations during the whole of 2005.
The group also said investigations into alleged human rights violations in Chechnya were ineffective and flawed.