Mikheil Saakashvili, Georgia's president, has defended his country's military assault on breakaway South Ossetia in August, saying Russian forces had invaded Georgia and its citizens were in danger.
Addressing a parliamentary commission investigating the war on Friday, he said: "We learned that Russian troops were moving through the Roki tunnel and had crossed the Georgian state boundary.
"I could not believe they would cross that red line... I could not believe they would be first to take this step.
"Our answer to the question whether we have undertaken military action is 'Yes', we took the decision to undertake military action."
The president, who has come under fire from opponents who accuse him of walking into a war that Georgia could not possibly win, said: "It was a difficult decision, but it was an inevitable one. Any democratic government would take the same decision, to protect its citizens."
Months of skirmishes between separatists and Georgian troops erupted into war in August when Georgia sent troops and tanks to retake the pro-Russian region of South Ossetia, which threw off Tbilisi's rule in 1991-92.
Moscow responded with a powerful counter-strike that drove the Georgian army out of South Ossetia.
Russian troops then pushed further into Georgia, saying they needed to prevent further Georgian attacks.
The West condemned the advance as a "disproportionate response".
In October, Russia pulled its troops back inside South Ossetia and Abkhazia, a second breakaway Georgian region, both of which Moscow has now recognised as independent states.
Russia blames Saakashvili for unleashing the conflict, but the Georgian president told the commission that Moscow was the aggressor.
He repeated previous statements that Tbilisi launched the full-scale assault on Tskhinvali, the South Ossetian capital, on the evening of August 7, having learned that Russian tanks and troops were pouring across the border and fearing for the safety of Georgian villages.
He said: "When we asked the Russians through the Americans what was the goal of their intervention, their answer was 'the complete destruction of Georgia'."