NOVOAZOVSK, Ukraine (AP) ― Pushing west in a new offensive along Ukraine’s strategic coastline, heavily armed Russian-backed separatist forces captured new territory Wednesday far from their previous battles with government troops.

The bold offensive along a new southeastern front raised the prospect that the separatists are seeking to create a land link between Russia and Crimea, which also would give them control over the entire Azov Sea.

After a third day of heavy shelling that sent many residents fleeing, rebel fighters with dozens of tanks and armored vehicles entered Novoazovsk, a resort town of 40,000 on the Azov Sea, the mayor said.

Novoazovsk lies along the road linking Russia to the Ukrainian port of Mariupol and onto Crimea, the Black Sea peninsula that Russia annexed in March.

The separatist attack appears to have caught government forces off guard, and they were scrambling Wednesday to build up defenses. The offensive also adds to growing evidence that the rebels receive Russian support.

Oleg Sidorkin, the mayor of Novoazovsk, said by telephone that the rebel forces had rolled into town from positions near Ukraine’s southernmost border with Russia.

To travel to this spot through Ukraine from the main front line around Donetsk and Luhansk, far to the north, the rebels would have had to cross territory controlled by government troops. 

The more logical conclusion is that they came across the nearby Russian border.

Ukraine and Western governments have long accused Russia of playing a direct role in the conflict, supplying troops and weaponry to the rebels. Russia consistently denies the claims, but its stance is increasingly dismissed abroad.

“Information, which in recent hours has gained another hard-facts confirmation, is that regular Russian units are operating in eastern Ukraine,” Polish Prime Minister Donald Tusk said Wednesday. “This information, coming from NATO and confirmed by our intelligence, is in fact unequivocal.”

The U.S. government accused Russia on Wednesday of orchestrating a new military campaign in Ukraine that is helping rebel forces expand their fight and sending in tanks, rocket launchers and armored vehicles.

“These incursions indicate a Russian-directed counteroffensive is likely underway in Donetsk and Luhansk,” State Department spokeswoman Jen Psaki told reporters. She also voiced concern about overnight deliveries of materiel in southeast Ukraine near Novoazovsk and said Russia was being dishonest about its actions, even to its own people.

Russian forces, she said, are being sent 48 kilometers inside Ukraine, without them or their families knowing where they are going. She cited reports of burials in Russia for those who have died in Ukraine and wounded Russian soldiers being treated in a St. Petersburg hospital.

Associated Press journalists on the border have seen the rebels with a wide range of unmarked military equipment ― including tanks, Buk missile launchers and armored personnel carriers ― and have run into many Russians among the rebel fighters. Ukraine also captured 10 soldiers from a Russian paratrooper division Monday around Amvrosiivka, a town about 20 kilometers from the Russian border.

On Wednesday, AP reporters saw more than 20 shells fall around Novoazovsk in a one-hour span. Many people were leaving the town, while others were rushing back in to evacuate relatives. Later in the day, access from the west was blocked by Ukrainian soldiers and the presence of rebels in Novoazovsk could not be independently confirmed.

A spokesman for Ukraine’s security council, Col. Andriy Lysenko, said he had no information that Novoazovsk had been occupied. Earlier, he said the shelling around the town was coming from both Ukrainian and Russian territory. Ukrainian security officials said nearby villages had also come under shelling.

The artillery shells in Novoazovsk appeared to be flying between rebel and government positions.

“It hit a tree, there was a blast and the shrapnel came down here,’‘ said Alexei Podlepentsov, an electrician at the Novoazovsk hospital, which was struck by shelling Tuesday.

In Mariupol, a city of 450,000 about 30 kilometers to the west, defenses were being built up. A brigade of Ukrainian forces arrived at the airport on Wednesday afternoon, while deep trenches were dug a day earlier on the city’s edge. Other troops were blocking traffic from leaving the port heading east.

Ukraine has already lost more than 750 kilometers of coastline in Crimea, along with a major naval port and significant mineral rights in the Black Sea.

If the separatists were to seize a land bridge to Crimea that would be a further loss of more than 250 kilometers of coastline. This would also give them or Russia control over the entire Azov Sea and any offshore oil and gas reserves.

This would leave Ukraine with about 450 kilometers of coastline to the west of Crimea.

Fighting also persisted elsewhere Wednesday, and Lysenko said 13 Ukrainian troops had been killed over the past day.

In Donetsk, the largest rebel-held city further north, at least three people were killed on a main road when their cars were hit by shrapnel from falling artillery shells.

Russian President Vladimir Putin and his Ukrainian counterpart, Petro Poroshenko, met Tuesday for their first one-on-one meeting, but there was no indication of a swift resolution to the fighting that has claimed at least 2,000 civilian lives.