KAMENSK-SHAKHTINSKY, Russia - Dozens of heavy Russian military vehicles massed on Friday near the border with Ukraine, where a huge Russian convoy with humanitarian aid came to a halt as Moscow and Kiev struggled to agree on border crossing procedures.
Russia says it is carrying 2,000 tonnes of water, baby food and other aid for people in east Ukraine, where pro-Moscow separatists are fighting government forces.
Kiev and some Western officials have said they believe the convoy could be a cover for a Russian military incursion - a claim Moscow has described as "absurd".
On Thursday, the convoy of some 280 trucks stopped in open fields near the Russian town of Kamensk-Shakhtinsky, about 20 km (12 miles) from the border with Ukraine.
It was still stationed there on Friday morning and a Reuters reporter at the scene saw a dozen armoured personnel carriers (APCs) on the move not far from the convoy.
Another Reuters reporter saw two dozen APCs moving near the border with Ukraine on Thursday night.
The Guardian reported on Friday its reporter saw several APCs crossing the border with Ukraine.
The newspaper said the move was unlikely to represent a full-scale official Russian invasion, but it was clear evidence that Russian troops are active inside Ukraine's borders.
Kiev and NATO have said they fear Russia will invade east Ukraine after massing more than 40,000 troops near the border.
Russia says it is conducting military exercises and has no plans to invade. It also denies supporting rebels in eastern Ukraine with arms and funds.
The United States and the European Union have imposed sanctions on Russia over its role in east Ukraine and the earlier annexation of Ukraine's region of Crimea, in what has become the worst crisis in relations between Moscow and the West since the Cold War.
Kiev has said if the humanitarian convoy enters Ukraine without the consent of the authorities, the Ukrainian government would view that as an illegal Russian incursion, further heightening tension.
However, there is still a possibility that a deal could be brokered. Russia's foreign ministry said it was in intensive negotiations with the Ukrainian government and the Red Cross.
A senior official of the Red Cross arrived in Kiev on Thursday for talks on aid.
Relief agencies say people living in Luhansk and in Donetsk face shortages of water, food and electricity after four months of conflict, in which the United Nations says more than 2,000 people have been killed.
Kiev blames Russia and the separatists for the plight of the civilians, but their situation has grown more acute as the Ukrainian military has pressed its offensive - including in areas where civilians live.
Artillery shells hit close to the centre of Ukraine's separatist-held city of Donetsk for the first time on Thursday.