Reports on Saturday described Russian soldiers digging trenches near Georgia's main Black Sea port of Poti, while Moscow said it had set up checkpoints in a "security zone" extending beyond South Ossetia into undisputed Georgian territory.
Gordon Johndroe, the US White House spokesman, said: "It is my understanding that they have not completely withdrawn from areas considered undisputed territory and they need to do that."
David Miliband, the UK's Foreign Secretary, said he was "deeply concerned" that Russian forces had not withdrawn to their positions before the outbreak of hostilities, as agreed.
Dmitry Medvedev, Russia's president, had said his troops would pullback to Georgia's two breakaway regions by Friday night.
"The pullout was carried out without any incidents and was completed according to plan at 15:50 GMT," the Russian statement said.
"Russian military columns proceeded to the territory of South Ossetia. A part of these units is already at its permanent bases on Russian territory."
"Peacekeeping checkpoints in the security zone have started carrying out the tasks set before them. In this way, the Russian side has implemented the agreements set out in the Moscow principles by Medvedev and [French President Nicolas] Sarkozy," it said.
General Nikolai Uvarov, a Russian military spokesman, said at least 40 Russian military vehicles left the strategic crossroads city of Gori in central Georgia, heading north toward Russia.
However, he said it would take some time to get all Russian personnel out.
"There are very many troops there right now. Troops or uniformed people, let's say, you cannot move them out immediately. There is just one road, one tunnel, one lane each way."
A senior Georgian official accused Russia of lying about having completed its troop pullout, saying Russian forces still occupied areas of the country.
"It is not true that the withdrawal is complete"
Shota Utiashvili, Georgia's interior ministry spokesman
"It is not true that the withdrawal is complete," Shota Utiashvili, Georgia's interior ministry spokesman said, adding that Russian forces continued to hold positions in the west of the country.
"They cannot stay in Senaki and Poti. Their presence there is illegal," he said.
The Pentagon also said in a statement that it still sees no clear sign of substantial Russian withdrawal from Georgia.
Gordon Johndroe, a White House spokesman, added that George Bush, the US president, and Sarkozy discussed the situation in Georgia on Friday and agreed "Russia is not in compliance and Russia needs to come into compliance now."
Russia says 500 "peacekeepers" are to remain in a buffer zone around South Ossetia.
An unknown number of combat troops also remain inside South Ossetia as well as Abkhazia, which both broke away from Tbilisi in the 1990s.
Russia will retain control over a road linking Tbilisi, the Georgian capital, to the sea even after completing the withdrawal, a map shown to journalists by a Russian general indicated.
The map, displayed at a news conference by Anatoly Nogovitsyn, deputy chief of general staff, shows Russia's self-imposed "zone of responsibility" to include stretches of Georgia's main east-west road.
These include most of the route from Georgia's main commercial port of Poti to the town of Senaki, where Nogovitsyn said troops would occupy the military aerodrome.
One hour prior to the Russian deadline of pulling out, Jonah Hull, Al Jazeera's correspondent in Tblisi, confirmed that the vast majority of Russian forces had pulled out from Gori.
"We saw a massive convoy of withdrawing Russian troops, armour, even soup kitchens and ambulances. They did look as if they were pulling out and pulling our proper.
"Georgian police are now ready to go into Gori," Hull said.
Russian troops entered Georgia in response to a Georgian offensive on August 7 to reassert control over South Ossetia, which broke away from Tbilisi in the early 1990s after the collapse of the Soviet Union.
The United Nations Security Council remained at odds on Friday over a draft resolution backing a European Union-sponsored ceasefire plan signed by both Russia and Georgia.
The US, France and Britain have been insisting on an immediate withdrawal by Russian forces as well as a commitment from Moscow to respect Georgia's territorial integrity.
However, Russia has drafted a second alternative resolution which restates and endorses the six-point peace plan.
|Churkin said he would seek a deal restating the six-point peace plan [AFP]
"Our draft resolution is a reconfirmation of the six-point agreement, and there's no territorial integrity in the six principles," Vitaly Churkin, Russia's ambassador to the UN, said after a council meeting on Thursday.
"We believe the six principles are clear and already implemented."
Alejandro Wolff, US deputy ambassador to the UN, said that Washington would not be able to support the Moscow draft and questioned whether Russia was trying to "strangle" the Georgian government.
"We have a presence of so-called Russian peacekeeping forces at key Georgian choke points that will control economic life, it will control humanitarian activities ... That's why clarifications are so important."
The ceasefire pact demands that both Russian and Georgian troops move back to positions they held before fighting broke out August 7, but Russian forces also can be in a security zone that extends 7km into Georgia from South Ossetia.
They are also allowed a presence on Georgian territory in a security zone along the border with Abkhazia, another separatist Georgian region, under a 1994 UN-approved agreement that ended a war there.