Hundreds of trucks carrying goods between Russia and Ukraine are unable to cross the border after Moscow Sunday ordered Ukrainian trucks be stopped from entering its territory and Kiev Monday responded in kind. It’s the latest move in a tit-for-tat trade war that shows no sign of abating as fighting continues in eastern Ukraine.

Ukrainian activists have blocked Russian trucks from crossing into Belarus as well as Hungary and Slovakia since last week, prompting Russian Prime Minister Dmitry Medvedev to describe them as “extremists” and accuse the government in Kiev of not being able to control its territory.

“Some people of unsound mind are attempting to stop all our heavy haulers,” the official Russian news agency Tass quoted Medvedev as saying Monday. “You and I understand: The Ukrainian state regrettably unable to instill order is responsible for all developments in its territory.”

Russia’s transport ministry said 100 of its trucks were blocked in Ukraine, while more than 500 will now not be able to cross into Ukraine on the way back to Russia from the European Union. The Ukrainian government said Russia had detained 152 trucks registered in Ukraine, the Associated Press reported.

Ukrainian Prime Minister Arseniy Yatsenyuk said Kiev would lift its ban when Moscow allows Ukrainian truckers back into its territory. The truck ban comes after similar trade moves with blocks on agricultural products and airline transportation between the two nations.

Relations between the neighboring countries have fallen to a new low after Russia annexed Crimea from Ukraine in March 2014 and a conflict pitting Ukrainian government troops against Russian-backed rebels has destroyed large parts of eastern Ukraine and left more than 9,000 people dead. Fighting again flared over the weekend with the head of the Organization for Security and Cooperation in Europe, the group monitoring the conflict, describing the humanitarian situation there as “dire.”

“It’s still, unfortunately, an active conflict,” said OSCE Secretary General Lamberto Zannier, according to Radio Free Europe/Radio Liberty. “We see ... ongoing military activities, especially on the separatist side, we’ve seen rather large night exercises — military exercises. So there is a lot of dynamic, a lot of movement there, and that’s of course a concern.”