MOSCOW • The war in eastern Ukraine that simmered quietly for months has erupted in a lethal bout of fighting in recent days.
The violence, which killed at least eight Ukrainian soldiers and three on the pro-Russian side, shifted the front lines by only a few hundred metres in several spots, but potentially complicates the United States' efforts to improve relations with Russia.
The US Army helps to train and equip Ukrainian soldiers, who are fighting Russian-backed separatists in two eastern provinces of Ukraine.
In the latest outbreak, the sides vied for control of what are known as "grey zone" territories, areas between the front lines that had previously been in buffer zones.
The Ukrainian army advanced in at least two places, according to news reports and official Ukrainian accounts, but it said it did so to rebuff rebel attacks. Each side blamed the other for the escalation.
Referring to one front-line town, Mr Yuri Kasyanov, an adviser to the Ukrainian Interior Ministry, told Radio Free Europe on Tuesday that "of course, the defenders of Avdiivka preferred to advance the line" to a more defensible position.
Ukraine's Foreign Affairs Ministry issued a statement appealing to Western governments to intervene diplomatically.
The statement said that "for the last two days, the Russian occupation forces carried out massive attacks across the line", firing with rocket artillery, heavy mortars and other long-range weapons. European monitors reported heavy shelling of Avdiivka since Sunday.
Journalists who visited the town reported evidence of a psychological warfare operation of a sophistication that suggested Russian involvement. Mobile phones in the town received text messages addressed to Ukrainian soldiers, who often carry phones, which read: "You are just meat to your commanders."
The shelling disrupted electrical and water supplies. The Ukrainian authorities set up heated shelters for residents whose homes had been damaged, as night-time temperatures dropped to as low as minus 28 deg C.
"Given harsh weather conditions and the continuing shelling by the militants, the humanitarian situation in the area continues to deteriorate," the Foreign Affairs Ministry's statement said. The authorities said they were preparing to evacuate the town's 16,000 residents.
The rebel governments of the Luhansk and Donetsk people's republics, which are not recognised internationally, issued a joint statement addressed to Russian President Vladimir Putin and US President Donald Trump that called for a diplomatic solution.
The Trump administration's manoeuvring for better relations with Russia has alarmed Ukrainian officials, who fear that Western pressure could ease on Russia to withdraw its unacknowledged military forces in eastern Ukraine.