(CNN) — Tensions are mounting at the border between Ukraine and Moscow-allied Belarus, as officials in Kyiv warn of a Russian spring offensive amid ramped-up military attacks from the Kremlin.

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.

Ukraine shares a 1,000-kilometer frontier with Belarus, a country that has played a key role in aiding Russia’s attack.

CNN’s Frederik Pleitgen and his team were 100 meters 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.

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.

Kyiv 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.”

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.

Anton Bychkovski, a spokesperson for Belarus State Border Committee, said the situation at the border was “tense,” with what he described as numerous provocations from Ukrainian armed formations.

“Mainly, there are attempts to reconnoiter the territory of Belarus with the help of drones,” he said from the Belarusian border town of Dyvin.

“We registered more than 400 instances of such attempts last year. Ukrainian forces sent drones alongside the border with Belarus, at times violating the air space. Technical means available for defense of Belarus allow us to counter such means of reconnaissance. Often such drones are forced to land in Belarus,” he added.

He said Belarusian border guard units have been expanded and “the armament and equipment were updated.”

According to their intelligence, “at the territory of the Ukrainian border regions there are about 17000 servicemen of the armed formations of the territorial defense of Ukraine which create certain challenges for security of the border of Belarus,” he said.

Earlier this month, the Belarusian defense ministry said a two-week joint air force exercise between Belarus and Russia, which took place from January 16 to February 1, had concluded.

Separately, the ministry announced the start of a week of joint military drills with Russia for the combined command of their regional grouping of forces. The ministry said it is in preparation for the joint Union Shield 2023 exercises the two countries will hold in Russia in September.

Belarusian President Alexander Lukashenko has repeatedly dismissed speculation that his troops would directly join the fighting across the border, but in December, Ukraine warned it does “not rule out” a “deliberate provocation” from Russia after Minsk said the wreckage of a Ukrainian missile landed on its territory.

In the Belarusian town of Kobryn, near the border with Ukraine, the war next door weighs heavily on its inhabitants.

“Of course, I am worried. This is a problem I was very worried about when it first happened, but I am an ordinary person I have no influence over this situation,” Diana Sychik, 28, told CNN. She begins to cry, saying she has not seen anything nor does she want to “engage in this conflict because this is bad, war is bad.”

She said her mother who lives near the border told her that tanks were being brought and saw helicopters flying.”But it is all understandable because our government also is worried for its people, and they had to secure the border somehow.”

An old man, who declined to provide his name, said he believed that “America is attacking us,” citing the HIMARS multiple launch rocket system supplied by the United States to Ukrainian forces.

“We are one nation with Russia. We absolutely should help them,” he said.

Tensions mount at the Belarus-Ukraine border amid concerns of a Russian spring offensive