Washington has accused Moscow of supporting separatists in eastern Ukraine with military hardware, including tanks.
A "fact sheet" released yesterday by the State Department says the U.S. has "no evidence that Russia’s support for the separatists has ceased," adding, "In fact, we assess that Russia continues to provide them with heavy weapons, other military equipment and financing, and continues to allow militants to enter Ukraine freely."
The fact sheet says Moscow continues to accumulate military equipment -- including a type of tank no longer used by Russian forces -- at a deployment site in southwest Russia.
"We are concerned much of this equipment will be transferred to separatists, as we are confident Russia has already delivered tanks and multiple rocket launchers to them from this site," the State Department said.
NATO said Russia had increased its soldiers on the frontier to some 10,000 to 12,000, up from less than 1,000.
A NATO official said the larger number of troops is "not a step in the right direction" but rather "a step away from de-escalating the situation."
President Petro Poroshenko held an emergency meeting with his leading security officials in Kyiv on July 14.
Afterward, he said that "information has...been confirmed that Russian staff officers are taking part in military operations against Ukrainian forces."
Poroshenko also said there is a need for tactical changes by Ukrainian forces to strengthen the defense of the border and protect people living near it.
With reporting by Reuters, AP, and dpa
That concludes our live blogging for Monday, July 14. Follow news from throughout RFE/RL's region HERE.
Reports now suggesting at least one person died in the downing of the Ukrainian military transport plane today:
(NOTE: Video contains graphic images.) Reuters has issued video after officials in the eastern Ukrainian city of Luhansk say that at least three people were killed in shelling there yesterday. One of the victims was a female guard at a school that was badly damaged in the strikes, while residents of apartment blocks said one of their neighbors was killed by shrapnel.
Comparisons of Vladimir Putin to Slobodan Milosevic are all the rage. But what does the Milosevic experience tell us about where Russia may be headed? Read Brian Whitmore's latest Power Vertical post, "Slobodan's Ghost."
Contradicting earlier suggestions that the crew could have numbered around 20, our Ukrainian Service quotes a National Security and Defense Council spokesman as saying there were eight people -- seven crew members and one person accompanying the equipment -- aboard the An-26 transport plane when it was downed. Ukrainian authorities said they were trying to locate and transport them to a location under Kyiv's control.