Pro-Russian rebels have attacked Ukrainian forces more than 100 times since Sunday, according to a report by UNIAN, a pro-Ukrainian English language news service. The attacks, most of which took place over a 6-hour period leading up to midnight on Sunday, have dramatically increased over the last month and are now reaching levels not seen since the Minsk II agreement ceasefire was signed in February, claims UNIAN.

"In [Ukraine's] Donetsk region, the militants fired 82mm and 120mm mortar shells [which are banned under the Minsk peace deal] repeatedly on Krasnohorivka, Maryinka, Avdiivka, Opytne and the Butovka mine,” the Ukrainian military said during a press conference in Kiev. “These settlements were also attacked by enemy tanks.”

The intensity and regularity of the attacks comes as a concern to the group of foreign ministers from Germany, France, Ukraine and Russia that have regularly met since the war began in April 2014 in an effort to bring the fighting in the contested region of Donbas, Ukraine, to a peaceful end. While once again suggesting last week that peace could be on the horizon, the ministers expressed deep concern that the fighting may soon spiral out of control, according to a press report from the French Foreign Ministry that recounted the minister's discussions.

And while those meetings have been successful in envisioning a roadmap on how to end the war, military actions on the ground have not followed suit. Just last week pro-Russian rebels launched a renewed attack on the strategic port city of Mariupol, Ukraine, a financial hub for the region's steel industry and a gateway port to the Black Sea. The coastal region had been largely peaceful over the last six weeks -- as most fighting took place on the demarcation line further inside Ukraine’s interior, near the de facto pro-Russian capital of Donetsk and the region's obliterated airport.

Those concerns were also echoed by NATO defense ministers that also met last week to discuss how the alliance should best deal with renewed Russian hostility across Europe.

"Violations of the ceasefire are still taking place, and there is a risk of the resumption of heavy fighting," said NATO Secretary General Jens Stoltenberg last week to defense ministers. "Russia continues to support the militants, providing training, weapons and soldiers. A large number of its troops are stationed on the border with Ukraine."