HALIFAX, Nova Scotia – A dispute over shipping lanes is threatening to reignite the 4-year-old simmering war between Ukraine and Russia following confrontations sparked by both sides in recent days.

Russian border guards on Monday detained Ukrainian fishing vessels in the Sea of Azov, a strategically important body of water contained to the north by Ukraine, to the west by the Crimean Peninsula and to the east and south by Russia. Monday's incident came days after Russian President Vladimir Putin slammed Kiev for detaining Russian commercial ships also in the Azov in what he described as "a totally illegal move" and which Kremlin officials have warned may prompt retaliation .

"It's a very deliberate attempt to raise the stakes," Ukrainian Defense Minister Pavlo Klimkin said Saturday on the sidelines of an international security conference that took place here. "It's about creeping annexation of the Azov Sea, but it's also about Crimea."

Crimea came under Russian control in 2014 through what Moscow says was a public referendum but what Kiev and its Western backers consider an illegal annexation. That same year, Russia began supporting separatist rebels in the eastern Ukrainian region known as Donbas. Klimkin estimates as many as 5,000 Russian forces and 1,500 tanks remain there.

Klimkin said the campaign in the Azov is designed to intimidate Ukraine and to disrupt its economic activities.

Twice last year, Russia shut off access to a key passageway to the Azov known as the Kerch Strait, and its ships have blocked ports in the Ukrainian towns of Berdyansk and Mariupol. The economic disruptions cost Ukraine as much as $40 million each year, according to an analysis by private intelligence firm Stratfor.

Kiev in 2016 filed a formal grievance to a tribunal in The Hague claiming that Russia's actions violate the 1982 United Nations Convention on the Law of the Sea. The proceedings are ongoing.

Both sides have indicated they're willing to further militarize the region. Ukrainian Prime Minister Petro Poroshenko pledged in September to build a naval base in the Azov before the end of the year. Kiev also took possession of two U.S. Coast Guard Island-class cutters earlier this year.

Though it doesn't have any permanent naval bases in the area, Russia has in recent months deployed at least 10 warships and 40 patrol boats to the Azov, Stratfor reports. Senior Russian political leaders have said they have no intentions of boosting the country's military presence there.

It's yet unclear how far the U.S. is willing to go in support for Ukraine. In a joint statement after Klimkin's meeting with Secretary of State Mike Pompeo last week, both sides "condemned Russia's aggressive actions against international shipping transiting the Black Sea, the Sea of Azov and the Kerch Strait to Ukrainian ports" and agreed that "Russia's aggressive activities in the Sea of Azov have brought new security, economic, social, and environmental threats to the entire Azov-Black Sea region."

The U.S. has continued sanctions against Russia, as well as lethal arms shipments and training programs for Ukrainian forces in retaliation for what it considers destabilizing activity in and around the region. However it's questionable – perhaps even doubtful – whether Washington would be willing to go to war with Russia over the former Soviet state.

Klimkin admits that the Ukrainian military is unmatched to take on Russia's increasingly sophisticated armed forces, but adds that his country is willing to fight back.