Tensions are mounting at the Belarusian-Ukrainian border amid concerns by Ukrainian officials about a Russian spring offensive. 

In rare access since Russia’s invasion of Ukraine last year, a CNN team visited Belarus’s southwest border near northwest Ukraine, accompanied by state border officials.

CNN’s Frederik Pleitgen and his team were 100 meters (more than 300 feet) away from the Ukrainian side, where they saw the Belarusian government’s fortification of the border area with barbed wire in a carefully orchestrated and tightly controlled press tour. 

According to the CNN team on the ground, the Ukrainian side of the border is heavily barricaded with several layers of barbed wire and earth mounds to stop anyone from going through.

Ukraine and Belarus share a 1,000-kilometer (more than 600 miles) frontier, much of it sparsely populated and thickly forested. 

Belarusian officials told CNN the border crossing from their side in the small town of Dyvin is still functioning but that the Ukrainian side has closed the crossing. 

Ukraine has closed all border crossings to Belarus, except to occasionally allow entry to Ukrainian refugees who are looking to return to their home country, out of concern Belarus could be used for a further invasion by Russia. 

The CNN team could see a Ukrainian flag on Ukraine’s side of the border crossing and a red and white flag which is associated with the Belarusian opposition — a move Belarusian authorities called a “provocation.” 

Some context: Russia used the territory of Belarus as one of its launch pads for the invasion of Ukraine in 2022. Joint military drills over the last year between Belarus and Russia have contributed to concerns that Belarusian troops could join Russia’s forces in Ukraine, but Belarusian President Alexander Lukashenko has repeatedly dismissed speculation that his troops would directly join the fighting in Ukraine. 

CNN’s Tim Lister contributed to this post.