Kiev (AFP) - The Ukrainian military on Sunday reported "intensive" movement of troops and equipment from Russia into the separatist controlled parts of eastern Ukraine.
"There is intensive deployment of military equipment and personnel of the enemy from the territory of the Russian Federation onto territory temporarily controlled by insurgents," Ukrainian military spokesman Andriy Lysenko told a briefing in Kiev.
In Donetsk, the main rebel-held city in Ukraine's industrial south-east, AFP reporters saw about 20 trucks, some carrying anti-aircraft guns, heading towards the government-held airport, although it was not clear whether these were new forces.
Several Western news outlets reported witnessing heavy movement of troops near Donetsk.
Among them, reporters for the news sites buzzfeed.com and mashable.com tweeted that they had seen a large military column. Buzzfeed's Max Seddon wrote: "31 unmarked Kamazes (military trucks) just drove past towards Donetsk. Anti-aircraft weapons, ammunition boxes, radar systems, a bus of gunmen."
Mashable's reporter Christopher Miller tweeted having seen more than 40 trucks headed toward Donetsk "with anti-aircraft guns, fighters".
Video footage that appeared on YouTube and was rebroadcast on Ukraine's Channel 5 -- but which could not be independently authenticated -- showed a huge column of green trucks snaking slowly through an unidentified city.
Russia has repeatedly denied accusations from Kiev, Western governments and the NATO alliance that it is fighting on the side of pro-Russian separatists who have taken over a swathe of Ukraine's industrial south-east.
However, Moscow openly supports the two self-declared rebel statelets politically and said it would recognise the validity of elections being held there Sunday.
The rebels, who also deny receiving help from Russia, have large amounts of sophisticated, heavy weaponry and no apparent problem in procuring ammunition. They have told journalists that some of their weapons are captured from Ukrainian forces.
A ceasefire was declared on September 5 in Ukraine but is violated daily in the conflict zone which runs along the Russian border. Rebel leaders say they intend to expand their territory as far as the Azoz Sea port of Mariupol.
Russian troops already occupy Ukraine's southern province of Crimea, which has been declared a part of Russia.
The province was taken over almost without a fight when large numbers of heavily armed men in unmarked uniforms quickly surrounded demoralised Ukrainian troops in March. The troops, widely dubbed "little green men", were later confirmed to have been Russian regular troops.