The US has accused Russia of again building up its forces along the border with eastern Ukraine, where fighting continues. Kyiv says its troops have battled separatists around three Ukrainian border towns.
The US Department of Defense on Wednesday said it had detected up to 12,000 Russian combat troops on Ukraine's eastern border and accused Russia of continuing to support separatists in eastern Ukraine.
In May, apparently in response to Western pressure, Russian reduced its border forces - put by the US at 40,000 - down to about 1,000.
But, in Washington on Wednesday, US defense spokesman Army Colonel Steve Warren estimated that 12,000 were present. He described the Russian units as "battalion task groups" and "combat soldiers"
"I can't speak for what they intend to do. Certainly, it is intimidating," Warren said.
Moscow has repeatedly denied sending advanced weapons being used by separatists since they were evicted by Ukrainian forces from their stronghold of Slavyansk 10 days ago.
Fighting around three border towns
Ukraine's Kyiv-based government on Wednesday said it had lost 11 servicemen in the past 24 hours during fighting around three towns close to Ukraine's border with Russia.
Ukrainian national security spokesman Andriy Lysenko identified them as the towns of Amvrosyika, Marynivka and Izvarne. Troops had been backed by Ukrainian artillery and aviation, he added.
Rebel leader Igor Strelkov said two of his fighters were killed during a rebel bid to cut off government forces east of Donetsk.
Lysenko said Ukrainian warplanes had been cleared to resume flights over the east. Two days ago, a government Antonov-26 transport plane was downed. Kyiv alleged that it was fired from Russia.
In Kyiv on Wednesday, new Ukrainian military recruits (pictured) to the self-defense battalion "Azov" swore allegiance before being sent to eastern Ukraine.
The office of German Chancellor Angela Merkel said earlier on Wednesday that she had had a telephone conversation with Ukrainian President Petro Poroshenko.
He had accused Russia of continuing to funnel weapons and militants into eastern Ukraine, his office said.
Truce efforts have been inconclusive. On Tuesday, a "contact group" of officials from Ukraine, Russia and the Organization for Security and Cooperation in Europe (OSCE) tried but failed to establish a video link-up with separatists.
Since losing Slavyansk, hundreds of rebel fighters have relocated to the industrial city of Donetsk, as well as vowing to make defiant stands. On Wednesday, rebels were sighted in Donetsk, loading their families onto Russia-bound buses.
Thousands of residents, fearing a government offensive, have fled the city, which had a pre-conflict population of nearly 1 million.
ipj/dr (dpa, AP, Reuters)