"Up to 70% of the municipal buildings have been damaged or completely destroyed," Robert Guliyev said. "The situation is almost the same in the private housing sector."
The mayor said around 15,000 civilians remained in the city, which had 30,000 residents before the attacks began.
Guliyev did not give the number of civilian deaths. According to Russia, around 1,600 civilians have died.
Colonel-General Anatoly Nogovitsyn, deputy chief of Russia's General Staff, said earlier Tuesday that all nurseries, schools and the only hospital in the city were destroyed on the first day of the attack.
The Defense Ministry official said Russia had provided the necessary financial assistance to rebuild Tskhinvali. Field bakeries have been set up in the conflict zone, and food and water are being supplied, he said.
Russian President Dmitry Medvedev ordered an end to the "peace enforcement" operation in Georgia earlier in the day, after five days of fighting that followed Georgia's military offensive to seize South Ossetia. However, he said Georgia must pull its troops back before a peace settlement can be reached.