A humanitarian aid convoy of around 260 Russian trucks covered in white tarpaulins arrived near the border with Ukraine on Thursday, stopping just short of crossing the frontier into the eastern Ukrainian region of Luhansk.

It wasn't clear on Friday when or if the convoy would cross the border into Ukraine, whose officials have expressed grave concerns about the humanitarian mission, saying they fear it could be at best a mere pretext for delivering arms to pro-Russia separatists in eastern Ukraine, or at worst cover for an incursion of Russian troops into Ukrainian territory.

Possibly adding to those fears are reports published by two British papers, which reported that a much smaller military convoy had actually crossed into Ukraine, around 200 kilometers (120 miles) from the eastern city of Donetsk.

According to The Guardian reporter's account, a column of 23 armored personnel carriers, along with fuel trucks and logistics vehicles took advantage of a gap in a barbed wire fence to cross into rebel-controlled eastern Ukraine using a dirt track.

It was not immediately clear what their intentions might be.

ICRC: talks ongoing

As for the stalled Russian aid convoy, Ukrainian officials have insisted that it would not be allowed to enter its territory until it had been inspected by an international organization.

Russia has said that it has been working with the International Committee of the Red Cross (ICRC) to facilitate the delivery of the aid, which the residents of Luhansk, who have been without water and electricity for almost a fortnight, desperately need.

However, an ICRC spokesperson said on Thursday, that talks with Russian officials were continuing, but that much still had to be cleared up before it could be involved in an operation to facilitate the distribution of the Russian aid.

"The plans keep changing, the discussions are going ahead and we will not confirm for sure until we know an agreement has been reached," spokesperson Anastasia Isyuk said from the ICRC's headquarters in Geneva.

Donetsk shelled

Meanwhile, shelling was reported in the center of Donetsk on Thursday, which Ukrainian government forces have been trying for weeks to recapture from pro-Russian rebels.

Despite being a close ally of the government in Kyiv, the United States called on Ukrainian forces to exercise restraint as they moved to retake the city.

"We call on the Ukrainians to take every step to avoid the local population as they try to free the city from the separatists," US State Department spokesperson Marie Harf said on Thursday.

pfd/ipj (dpa, AFP, AP)