Ukrainian troops are struggling to counter artillery fire and electronic jamming by pro-Russian militants, who are flying drones to target the Kiev government forces, a top US general said Thursday.

The Ukrainian army's communications are hampered by the electronic warfare carried out by the separatists and they lack equipment and training to thwart artillery barrages, Lieutenant General Ben Hodges told reporters via video link from Germany.

"It is very difficult for Ukrainian forces to be able to operate on radios, telephones and other non-secure means of communications because their opponents have such an exceptional amount of jamming capability," said Hodges, commander of US Army Europe.

"Even if you can acquire where mortar or rockets are coming from, to be able to do something about it is very difficult if you can't communicate."

Surveillance drones supplied by Russia are enabling the separatists to pinpoint the location of Ukrainian troops with deadly accuracy.

"The rebels have Russian-provided UAVs (unmanned aerial vehicles) that are giving the rebels the detection capability and the ability to target Ukrainian forces," the general said, speaking from an American base at Wiesbaden.

"So they've suffered heavy casualties from heavy artillery and from rockets."

The casualties are stretching the limits of the government army's medical services, which provides quality care but lacks the capacity to keep up with the stream of wounded troops, according to Hodges.

Hodges said planned US military instruction for Kiev's forces, which is due to start in the spring, could help alleviate the impact of the jamming and artillery fire, while also helping with emergency medical care.

The training, which will focus on units from Ukraine's interior ministry, will help local forces find "ways to avoid jamming" and to adhere to special procedures when using radios, Hodges said.

- US tanks to Europe -

The United States has accused Russia of conducting a proxy war in Ukraine but has so far ruled out arms deliveries to Kiev.

Instead, Washington has supplied the government with "non-lethal" equipment, including radar to detect mortar fire.

A different type of radar is needed to detect artillery rounds, Hodges said. But he stopped short of advocating providing weapons to the Ukrainians, as urged by some US lawmakers and the Kiev government.

Pro-Russian fighters last week withdrew from peace talks and announced a new offensive. The United Nations has estimated a death toll of 5,100 from the nine-month war in the country's east.

To reassure NATO allies anxious over a more assertive Russia, the United States has carried out high-profile exercises with Eastern European partners and sent in armored units for temporary deployments to the Baltics and Poland.

Hodges said a brigade from the US Army's 3rd Infantry Division would start arriving in March as part of the troop rotation. And in a reversal of a years-long drawdown of American forces in Europe, the brigade's entire fleet of tanks and armored vehicles will be transported to German or other European bases by the end of the year, he said.

The brigade's arsenal includes more than 200 M-1 Abrams tanks as well as Bradley fighting vehicles and Paladin 155mm howitzers, he said.