Georgia has signed a ceasefire agreement seeking to end its conflict with Russia.
'With the signing of this accord, all Russian troops, and any paramilitary and irregular troops that entered with them must leave immediately,' US Secretary of State Condoleezza Rice said in the Georgian capital Tbilisi.
Despite the accord brokered by French President Nicolas Sarkozy earlier this week Russian armoured vehicles and tanks remained deep inside Georgian territory, some even pressing further towards Tbilisi.
Ms Rice, whose visit to Tbilisi was seen as a show of support for President Mikheil Saakashvili's pro-Western government, criticised the Russians for not honouring their promises to halt military operations in Georgia.
'The verbal assurance that President (Dmitry) Medvedev gave that Russian military operations had stopped... clearly was not honoured,' Ms Rice said.
Scores of Russian armoured vehicles were concentrated at a base outside Gori, a strategically key town half-way between Tbilisi and the breakaway Georgian province of South Ossetia which was the spark for the conflict.
A convoy of 10 Russian armoured personnel carriers was seen move from Gori before stopping in a position just 40km from Tbilisi today, according to wire services.
Bush urges Russia to pull out troops
US President George W Bush meanwhile called on Russia to honour its pledge to withdraw its troops.
'Bullying and intimidation are not acceptable ways to conduct foreign policy in the 21st century,' he said, adding that Russia had damaged its credibility with the West by its offensive against Georgia.
'Moscow must honour its commitment to withdraw its invading forces from all Georgian territory,' Mr Bush said outside the Oval Office.
Russian troops entered Georgia in response to a Georgian offensive on 7 August to retake South Ossetia, which broke away in the 1990s.
Russia strongly supports South Ossetia and the second breakaway region of Abkhazia and has given Russian passports to most people in the territories.
'A significant part of Georgian territory remains under foreign military occupation,' Mr Saakashvili said alongside Rice.
'Never, ever will Georgia reconcile itself with the occupation of even one square kilometre of its territory,' Mr Saakashvili added.
Mr Rice said that the US favoured the deployment of a neutral international peacekeeping force in Georgia.
As tensions flared between Moscow and Washington, Mr Medvedev also clashed over the crisis with German Chancellor Angela Merkel during talks at the Black Sea resort of Sochi.
Medvedev defends Russia's actions
While he renewed his support for South Ossetia and Abkhazia, she slammed the Russians for their disproportionate use of force and said the territorial integrity of Georgia must be a basic point in any plan for restoring peace in the Caucasus.
Mr Medvedev was unrepentant at their joint news conference. 'If someone continues to attack our citizens, our peacekeepers, then of course we will answer just as we did,' the Russian leader said.
'Russia, as guarantor of security in the Caucasus and the region, will make the decision which unambiguously supports the will of these two Caucasus peoples,' Mr Medvedev said.
He said the separatist regions could not live under Georgian control again.
'Unfortunately after what has happened it is unlikely Ossetians and Abkhaz can live in one state with Georgians,' Mr Medvedev said.
UN says aid access is hampered
A second US military cargo plane filled with humanitarian supplies arrived in Tbilisi yesterday, as UN officials and aid organisations complained of a lack of access to affected areas.
UN Secretary General Ban Ki-moon expressed serious concern and underlined the 'critical importance of safe and unimpeded access for humanitarian actors to all conflict-affected areas'.
The latest estimate by the UN High Commissioner for Refugees put the number of displaced people in the conflict region at more than 118,000.
Armed gunmen held up UN workers in Gori yesterday and stole their vehicles, underlining the difficulty of bringing aid to areas where it was needed most.
