U.S. State Department spokeswoman Jen Psaki says reports from eastern and southeastern Ukraine "indicate that a Russian-directed counteroffensive is likely under way" against government forces in Ukraine's Donetsk and Luhansk regions.
Psaki said on August 27 that the reports include descriptions of "columns of Russian tanks, multiple rocket launchers, and armored vehicles pushing toward communities in southeastern Ukraine."
She said they also include reports of "heavy fighting and shelling near the city and airport in Donetsk."
Psaki said Washington was "concerned by the Russian government’s unwillingness to tell the truth, even as its soldiers are found 30 miles [50 kilometers] inside Ukraine" -- adding that "Russia is sending its young men into Ukraine but are not telling them where they are going or telling their parents what they are doing."
She also noted "reports of wounded Russian soldiers in a St. Petersburg hospital, and that other Russian soldiers are returning home to Russia for burial."
"These are not steps that certainly you take when you are operating in a transparent manner," she concluded.
Fighting On Southern Front
Ukrainian security spokesman Andriy Lysenko announced on August 27 that reinforcements were being sent to the town of Novoazovsk, on the Sea of Azov about 10 kilometers from the Russian border, after the local mayor said pro-Russian fighters entered the town with support from dozens of armored vehicles.
Reports from correspondents in the area on August 27, as well as messages on social media by pro-government Ukrainian fighters, said government forces had abandoned all of their checkpoints on the main road linking the separatist-held city of Donetsk to Novoazovsk.
The developments come two days after Lysenko claimed Russian tanks invaded southeastern Ukraine disguised as pro-Russian separatist fighters.
Lysenko said Russian artillery was continuing to support the battle on August 27 by firing across the border from Russian territory.
He also said a Russian "tactical battalion" -- a battlefield command-and-control unit -- was positioned on August 27 near Novoazovsk at the Ukrainian village of Pobeda.
Moscow denies sending troops into Ukraine, claiming Russian paratroopers captured by Ukrainian forces in recent days had "inadvertently" crossed the border.
Poroshenko: Minsk Talks 'Very Effective'
The latest allegations of Russian troop activity within Ukraine come a day after Russian President Vladimir Putin told Ukrainian President Petro Poroshenko in Minsk that Moscow will "do everything to support" a peace process in Ukraine "if it starts."
Poroshenko promised to draft a new cease-fire plan after his face-to-face talks with Putin, which came after a summit in Minsk that included EU foreign-policy chief Catherine Ashton, Kazakh President Nursultan Nazabaev, and Belarusian President Alyaksandr Lukashenka.
Poroshenko said in Kyiv on August 27 that the talks in Minsk were "very effective."
He told a meeting of his Solidarity Party, which has been renamed the Petro Poroshenko Bloc, that he "clearly stressed there will be no bargaining over sovereignty, territorial integrity, the independence of our country, [or] the sovereign choice of the Ukrainian people and their European choice."
Russian Foreign Minister Sergei Lavrov said on August 27 that Russia was not interested in breaking up Ukraine despite respecting declarations of independence by separatists in eastern Ukraine.
But in Warsaw, Polish Prime Minister Donald Tusk told parliament that "no one can take seriously" Russia's claims that it is not supporting the pro-Russian separatists in Ukraine.
In a phone call with Russian President Vladimir Putin on August 27, German Chancellor Angela Merkel said the reports of the presence of Russian soldiers in eastern Ukraine “must be explained," her spokesperson said.
Merkel also emphasized Russia's “major responsibility for de-escalation and watching over its own frontiers."
Meanwhile, Kremlin spokesman Dmitry Peskov said on August 27 that claims about an upsurge in Russian military activity on the border with Ukraine have "nothing to do with the reality."
Peskov added that Russia was ready to send a second humanitarian aid convoy to eastern Ukraine "even tomorrow."
An earlier convoy entered Ukrainian territory last week without Kyiv's permission, raising tensions between the West and Moscow.
Peskov also said Russia is and will be a reliable supplier of natural gas to Europe, following warnings from Kyiv that Moscow could cut off fuel to the continent this winter.
"We hope that Ukraine in turn will guarantee unhindered transit," he added.
Russian Troops In Ukraine
Meanwhile, the Ukrainian Security Service (SBU) held a press conference where it presented a group of Russian soldiers captured earlier this week after they crossed the border from Russia into Ukraine.
One soldier, identified as Corporal Ivan Romantsev, said the soldiers had not realized they had crossed the border into Ukraine.
He told journalists that what is being shown on Russian television "is completely different from what is really happening."
Ukraine's military first released a video showing the captured soldiers on August 26.
Russian Defense Ministry officials admitted on August 26 that Russian soldiers had crossed into Ukrainian territory but said they had accidentally crossed an unmarked section of the border.
The Associated Press news agency quoted the Finnish Foreign Ministry as saying the United States and Russia held secret talks on the Ukraine crisis in Finland in June.
Ministry spokesman Vesa Hakkinen said the ministry helped organize the meeting but declined to give more information.
The Russian Foreign Ministry on August 27 denied reports of secret talks, saying the meeting involved only representatives from nongovernmental organizations and academic communities and did not involve official state diplomatic contacts.
According to the United Nations, more than 2,000 people have died since April in fighting between Ukrainian forces and pro-Russian separatists in the eastern regions of Donetsk and Luhansk.
With reporting by Reuters, AFP, AP, dpa, ITAR-TASS, and Interfax