A US navy warship has arrived in Georgia's main Black Sea port of Batumi with humanitarian aid. The US aid comes as Russia ignores Western demands to remove its remaining troops from Georgia's heartland. Russia says the residual troops are peacekeepers needed to avert further bloodshed and to protect the people of Georgia's separatist, pro-Moscow provinces of South Ossetia and Abkhazia two days after Moscow said it had wrapped up its withdrawal. On Georgia's main east-west rail line, a fuel train exploded after apparently hitting a landmine. The conflict erupted on August 8 when Georgia tried to retake South Ossetia. A Russian counter-offensive pushed into Georgia proper, crossing its east-west highway and nearing a Western-backed oil pipeline. Russian troops also moved into Western Georgia from Abkhazia, another breakaway region on the Black Sea. Hundreds of people were killed, tens of thousands displaced and housing and infrastructure wrecked in the fighting. In Batumi, 80 km (50 miles) south of another port, Poti, where Russian troops are still present, the USS McFaul arrived with aid for the tens of thousands displaced by the conflict. Underscoring US support for Georgia, two other US ships are due to follow the guided missile destroyer to the port. The US has already delivered some aid by military cargo plane but is now shipping in beds and food. Russia's Black Sea fleet flagship vessel, the Moskva, is no longer in the same area, having returned to its base in Ukraine on Saturday, Russian news agencies reported. Georgian officials were assessing the scale of the damage from the fuel train blast, which could potentially disrupt a key trade route for oil exports from Azerbaijan to European markets. Prime Minister Lado Gurgenidze told Reuters by telephone: "The railway is vital not just for the Georgian economy but for the economy of neighbouring countries."