More than 10 people have been killed and dozens more wounded in some of the heaviest shelling in months between army and anti-government forces in southeast Ukraine, an outburst of violence that may provoke an early test of President Trump’s ability to manage negotiations with the Kremlin over the thorny conflict.

In Washington, the State Department on Tuesday called for an immediate cease-fire.

With temperatures as low as minus-4 , what Ukrainian officials described as Grad rockets and 152mm artillery shells have rained down for days on the city of Avdiivka, an industrial hub built around a sprawling coking plant that has hosted a grinding standoff in this three-year-old conflict. Ukrainian forces, who recaptured the town in 2014, have suffered high casualties in the latest spate of violence: eight dead and 26 others wounded in two days. Separatist forces said that two of their fighters had died and six had been wounded in the fighting. 

The latest round of violence occurred suddenly, and both sides have blamed the other for it.

“Today for the first time in days Grad rocket launchers and heavy artillery were used against the civilian population and our units,” Ukrainian President Petro Poroshenko said during a meeting with security officials Tuesday. “The shelling is massive.”

The situation has grown so dire that Ukrainian authorities have announced an evacuation of Avdiivka, the first of the city during the conflict.

Veronika Bahal, a press officer for the Ukrainian Ministry for Emergency Affairs in the Donetsk region, said by telephone that as many as 12,000 people may be evacuated by bus and light rail from the city beginning at 8 a.m. Wednesday. Conditions are difficult in the town, she said, which lacks electricity and running water.

The uptick in fighting came just days after Trump’s first telephone conversation with Russian President Vladi­mir Putin, when the two discussed the conflict in Ukraine and declared plans to improve relations. The fighting in Ukraine, where Russia is supporting anti-government separatists, and the war in Syria were the basis for a frigid relationship between Putin and former president Barack Obama.

Trump, meanwhile, echoed Russian talking points about Ukraine during the campaign, saying that Putin had not sent his military into the country and that most people in Crimea, the peninsula annexed by Russia in 2014, did not want to be a part of Ukraine.

The Ukrainian administration is eager to establish a relationship with Trump, counting on traditional Republican skepticism about Russia to persuade the new president to maintain badly needed U.S. support for Kiev. Ukrainian officials have floated a possible meeting between the two presidents in February, although it is not clear where or how that would be organized. 

There have been suggestions that the Kremlin would test Trump early in his presidency with an international crisis or take advantage of the chaos in Washington to consolidate gains in southeast Ukraine. But with Trump now occupying the White House, the Kremlin may see the negotiating table as the best way to get what it wants now: a repeal of the sanctions imposed after the annexation of Crimea and recognition of Russia as a great power that can dominate a sphere of influence that includes Ukraine. 

Mark Toner, the acting spokesman for the State Department, said that monitors from the Organization for Security and Cooperation in Europe (OSCE) had reported the use of heavy artillery and other weapons that are prohibited by the Minsk protocols, which were supposed to provide a road map out of the crisis but have increasingly gone ignored. He said a cease-fire was necessary to avoid a larger humanitarian crisis, and he reaffirmed American support for the Minsk agreement.

A miner sits in an ambulance Tuesday in Donetsk, Ukraine, after being evacuated from a mine that lost power, reportedly because of shelling in the region, which pro-Russian separatists control. (Alexander Ermochenko/European Pressphoto Agency)

The conflict has left more than 10,000 dead since April 2014. Little territory has changed hands in the war since February 2015, when the separatists seized the town of Debaltseve in a bloody advance, but flare-ups in the form of artillery duels have occurred periodically.

There was no sign that the violence was slowing by Tuesday night. Reached via an electronic messaging app, Musa Magomedov, the head of Avdiivka’s coking plant, said there was still “a lot of firing.”

Magomedov said that the gas at the plant was being used to heat water for the town but that the plant urgently needed deliveries of natural gas or would have to shut down.

Kremlin spokesman Dmitri Peskov told journalists the violence was “a provocation.”

At an emergency meeting of the OSCE Permanent Council in Vienna, U.S. Charge d’Affairs Kate Byrnes, a 24-year veteran of the State Department, blamed the violence on “combined Russian-separatist forces.”

“We call on Russia to stop the violence, honor the cease-fire, withdraw heavy weapons, and end attempts to seize new territory beyond the line of contact,” she said.  

Karen DeYoung in Washington contributed to this report.