At least 25 people have died since fighting first broke out on Wednesday, as Russian troops began an offensive to flush out separatist fighters near the southeastern town of Avtury.
And at least 18 of those rebels and three Russian soldiers died as some 100 fighters fought off more than 500 troops around the town that rests in the foothills of the mountains that hug Chechnya's southern border, Russian news agencies reported.
As the fighters retreated into the peaks, they killed the head of the pro-Moscow administration at Tsa-Vedeno, a village that sits alongside the main highway that leads into the hills from Avtury, the Interfax news agency reported.
Masked men in camouflage uniforms shot at Sulyan Usupov as he headed to work, killing him on the spot, a regional administration official told Interfax.
A soldier was also killed on Thursday when fighters shot at a military vehicle that headed to the scene to investigate Usupov's killing, military officials said.
Meanwhile the campaign ahead of the Kremlin-organized October presidential elections in Chechnya heated up, with a leading candidate charging that the lists of registered voters have been padded.
Of the more than 540,000 supposed voters, "nearly 200,000 are ... dead souls" who exist only on paper, Aslambek Aslakhanov, the republic's deputy in Russia's lower house of parliament said.
But an official of Chechnya's current pro-Moscow administration, which prepared the voter lists, dismissed Aslakhanov's charges as a "security measure in case he loses".
"Why hasn't Aslakhanov said anything before?" said the official, who did not want to be identified.
''Of the more than 540,000 supposed voters, nearly 200,000 are... dead souls who exist only on paper"
Chechnya's deputy in the Russian parliament
Human rights organisations and other candidates have also previously questioned the validity of the voter lists.
Aslakhanov is one of 11 candidates running for president in elections scheduled for 5 October, the electoral commission said on Thursday, revising its earlier figure of 13.
The poll comes four years after Russian troops poured into the republic to put down what Kremlin called a separatist insurgency, the second such war between Russian federal forces and Chechen separatists in a decade.
Moscow has showcased the election as proof that the military conflict in Chechnya is over, efforts that have been belied by increased separatist activity in Chechnya and southern Russia as well as suicide attacks in Moscow.