TBILISI/SOCHI U.S. President George W. Bush denounced Moscow's actions in Georgia as unacceptable on Friday while Russian troops made their deepest incursion into Georgian territory since the conflict began last week.
Georgian President Mikheil Saakashvili said he had signed a ceasefire agreement, negotiated by France on behalf of the European Union, but Russia said it would not comment until it had seen his signature on the document.
"The time for conversations has passed. The time for concrete action has come," Russian news agency Interfax quoted an unidentified, high-ranking source in the Ministry of Foreign Affairs as saying.
About 17 armored personnel carriers and about 200 soldiers advanced to a village 45 km (30 miles) from Tbilisi, the deepest drive into Georgian territory since fighting began in Georgia's breakaway region South Ossetia on Thursday.
The vehicles traveled unimpeded by Georgian police and army stationed along the road. A Reuters correspondent saw a military ambulance, snipers and rocket-propelled grenades.
Saakashvili said tanks also advanced on another two towns -- Khashari and Borjomi -- in central Georgia, but that could not be independently verified.
A reason for the presence of Russian armor maneuvering inside Georgia in either case was not immediately clear.
Bush said: "The world has watched with alarm as Russia invaded a sovereign neighboring state and threatened a democratic government elected by its people.
"This act is completely unacceptable to the free nations of the world," Bush said in his weekly Saturday radio address, which the White House released on Friday.
The United States earlier demanded Russian troops end their occupation of Georgia immediately after Georgia signed the ceasefire agreement.
Speaking alongside Saakashvili in Tbilisi, visiting U.S. Secretary of State Condoleezza Rice evoked the Soviet-led invasion of Czechoslovakia 40 years ago: "Russian forces need to leave Georgia at once. This is no longer 1968."
Saakashvili met with Rice for five hours.
Saakashvili, in passionate remarks, denounced Russians as "21st century barbarians" and blamed the West for triggering the crisis by failing to react firmly to Moscow's previous military moves and not admitting Georgia to NATO fast enough.
"Who invited the trouble here?" he said, flanked by several large Georgian and U.S. flags. "Not only those people who perpetrated this, but those who failed to stop it."
The simmering crisis over the rebel Georgian region of South Ossetia exploded when Georgia tried to retake the Russian-backed province, provoking a massive counter-attack by Moscow.
The Kremlin deployed warships, planes, tanks and troops against Georgia in its biggest military operation outside its borders since the 1991 fall of the Soviet Union. Its troops continue to occupy part of Georgia, although combat has ceased.
Signs multiplied on Friday of Russia's growing international isolation. Its biggest trading partner Germany condemned it for going too far in Georgia and neighboring Poland sealed a pact with Washington to host part of an anti-missile system.
Russian President Dmitry Medvedev showed defiance after meeting German Chancellor Angela Merkel in the Black Sea resort of Sochi, along the coast from the conflict zone.
He said Moscow would respond the same way if its peacekeepers were attacked again and questioned whether the rebel regions at the centre of the conflict could ever live again under Georgian rule.
Medvedev also denounced the Polish-U.S. deal as a threat to Russia. "The deployment of new anti-missile forces has as its aim the Russian Federation," he told a news conference alongside Merkel.
"Therefore any fairy tales about deterring other states, fairy tales that with the help of this system, we will deter some sort of rogue states, no longer work."
Merkel also called on the Kremlin to pull its forces out of central Georgia and implement the French-led peace plan.
"We very much want the six-point plan to be implemented very promptly so that Russian troops are no longer in Georgia, outside Abkhazia and South Ossetia," she told the joint news conference with Medvedev.
Pressure from Berlin is significant because Moscow generally regards it as a more sympathetic partner than former Cold War foes London and Washington.
The conflict has rattled oil markets because a key pipeline runs through Georgia. It has also unnerved the West, which fears the conflict could easily escalate in the volatile region.
Russia says its actions are fully justified by Georgia's "aggression" and "genocide" in attacking South Ossetia last week, where many residents hold Russian passports.
It maintains its troops must stay in Georgia to secure the situation and prevent further conflict. Russian ground forces are mainly based around the central town of Gori, 70 km (40 miles) west of the Georgian capital.
In Moscow, the General Staff said at its daily news briefing that there had been no shooting in the past 24 hours.
Russia says 1,600 civilians died when Georgia attacked South Ossetia, though the figure has not been independently verified.
Moscow's General Staff has said it lost 74 soldiers in the fighting, with 171 wounded and 19 missing. At least four warplanes have been shot down.
Georgia puts deaths on its side at more than 175, with hundreds injured. That figure does not include South Ossetia.
(Additional reporting by James Kilner in Igoeti, Margarita Antidze and Matt Robinson in Tbilisi and Tabassum Zakaria and Richard Cowan in Washington; Writing by Chris Baldwin in Moscow, editing by Mary Gabriel)