TBILISI, Georgia (CNN) -- A train carrying fuel hit a mine and burst into flames near the Georgian city of Gori Sunday morning, according to an Interior Ministry spokesman.
The explosion, which happened on the railway tracks in the village of Skra, caused a huge fire, the spokesman said. A television report said 10 tanker cards were on fire, according to The Associated Press.
There were no immediate reports casualties, but reports said two houses were damaged and windows were blown out, AP reported. Georgian Interior Ministry spokesman Shota Utiashvili blamed Russia for the blast.
In another development Sunday, a U.S. Navy warship carrying humanitarian aid anchored in the southern Georgian port of Batumi on Sunday, AP reported.
The move sends a signal of support to Georgia in a two-week old struggle with Russia over the breakaway province of South Ossettia that has seen Russian troops drive deep into Georgian territory.
Most Russian troops have withdrawn from eastern and western Georgia, but they still maintain some checkpoints in the country, a spokesman for Georgia's Interior Ministry said Saturday. Watch Russian troops dig in »
Georgian police were resuming control of the city of Gori after Russian troops departed, and internally displaced people were returning, said Shota Utiashvili, an Interior Ministry spokesman.
Russian troops no longer controlled a key east-west highway, Utiashvili said, but they maintained checkpoints in the Black Sea port of Poti. The port is outside of of South Ossetia, a Georgian separatist region that is at the heart of the conflict.
In Moscow, Russian military spokesman Col. Gen. Anatoly Nogovitsyn, said Saturday that some Georgian troops were preparing caches of weapons for "further activity," though he offered no additional detail.
The comments came a day after Russia said it had withdrawn its forces from Georgia into the breakaway Georgian region of South Ossetia, completing its end of the cease-fire agreement reached last weekend. Yet Georgian and U.S. officials were quick to say Russia was not keeping its end of the deal.
Georgia's interior ministry said Friday that the Russians were "just changing hats" to make themselves look like peacekeepers.
And U.S. Deputy State Department spokesman Robert Wood said the Russians "without a doubt have failed to live up to their obligations under the ceasefire agreement."
An immediate concern expressed by all sides involved buffer zones outside of two Georgian breakaway provinces, South Ossetia and Abkhazia. Russia insists it has the right to create these zones under the cease-fire deal, but Wood said, "Establishing check-points and buffer zones are definitely not part of the agreement." Watch more on Russia's withdrawal »
The six-point cease-fire deal established that, while the two sides await an international peace monitoring mechanism, Russian forces will take "additional security measures."
In a letter clarifying that point, French President Nicolas Sarkozy -- who helped broker the deal -- wrote that such measures "may only be implemented in the immediate proximity of South Ossetia to the exclusion of any other part of Georgian territory."
He added that the measures must be "inside a zone of a depth of a few kilometers from the administrative limit between South Ossetia and the rest of Georgia in a manner such that no significant urban zone would be included."
Russia has argued that its peacekeeping forces, who are in the breakaway regions under previous agreements, need protection from the Georgian military. Georgia has said the peacekeeping troops are under no threat, and that Russia's real intent is to expand its military presence in Georgia.
The commander of Russia's land forces, Gen. Vladimir Boldyrev, said Russian peacekeeping troops would be stationed at posts that troops have been constructing since the invasion, some of them inside Georgian territory. Russia argues that it is allowed to expand its security zone under a 1992 agreement.
Russian Defense Minister Anatoly Serdyukov said Friday that Russia's withdrawal took place "without incident," according to a report by the Interfax news agency. "So the Russian side has complied with the agreements recorded in Moscow's Medvedev-Sarkozy principles," Serdyukov added.
But Georgia's Interior Ministry said the Russian peacekeeper checkpoints are farther into Georgia than the peace agreement allows. The ministry said it is trying to determine where the checkpoints are, and whether they are permanent or temporary.
The Organization for Security and Cooperation in Europe (OSCE) believes the buffer zones should be 7 kilometers (4 miles) wide.
Russia, meanwhile, accused Georgia of violating the cease-fire deal, partly by conducting operations into South Ossetia this week. Nogovitsyn, the Russian military spokesman, said agents from Georgia's interior ministry used physical force to question two Ossetians about Russian forces on Monday.
Georgia denied the accusation, saying it has no presence in South Ossetia.
A CNN producer outside the capital, Tbilisi, on Friday saw some Russian soldiers making slight changes to their military uniforms -- adding a white armband to appear as peacekeepers.
Nogovitsyn also said that the Russian military has suspended cooperation with NATO because of the rift over Georgia. Russia opposes Georgia's desire to join NATO.
Nogovitsyn has questioned why ships from NATO nations have sailed into the Black Sea in recent days. He said Saturday that ships from Germany, Poland, Spain and the United States were in the area. Watch more on Russia and NATO »
"There is a chance of escalation over the Black Sea feet," he said. "The NATO countries continue to step up their presence ... I don't think this will help to stabilize the situation in the region."
Russia's incursion into the former Soviet republic followed the launch of a Georgian campaign against the Russian-backed separatist territory of South Ossetia on August 7.
Most of the fighting has been centered in pro-Moscow South Ossetia, where Russian and Georgian soldiers fought street by street, destroying buildings and splitting up families.
CNN's Phil Black contributed to this report
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