Russia allegedly is providing artillery weapons to rebels in Ukraine trying to take Mariupol, a strategically important seaport. Col. Viktor Shidlyukh, the deputy commander of Ukrainian forces defending Mariupol, said the rebels recently started using the artillery weapons for the first time, the Telegraph reported. 

The weapons appear to be "air burst" artillery, which uses a delayed charge to detonate the shell before it reaches the ground, showering the target with shrapnel. Military officials claim Russia provided the weapons to the rebels amid a ceasefire agreement that has largely been ignored after Ukrainian troops lost the town of Debaltseve last week.

Russia has said it is not helping the rebels while Ukrainian officials say Russian troops are fighting in Ukraine. A military train transporting 60 armored vehicles including tanks reportedly arrived in the town of Amvrosiivka from Russia Saturday.

Mariupol is home to 500,000 people and is the biggest government-held city in the two rebellious provinces. The city has braced for a separatist invasion for months, with roadblocks and checkpoints at every entry road.

“Right now, we are building a strong defense line around the city. And it would help to build another defense line,” Mariupol Mayor Yuriy Khotlubei told the Washington Post. “It won’t be that easy for them to get into the city.”

Residents said they were prepared to defend Mariupol from the rebels. “I will stay and fight, if the war comes to my city,” said Anatoly Bezruchko, 62. “You can’t just live to eat and sleep. You have to defend your homeland.”

U.S. Secretary of State John Kerry said Saturday Western leaders were weighing new sanctions against Russia because of the ceasefire violations. "In the next few days I anticipate that President Obama will evaluate the choices that are in front of him and will make his decision as to what the next step will be," Kerry told a news conference. "There are serious discussions taking place between us and our European allies as to what those next sanctions steps ought to be and when they ought to be implemented."