Ukraine says it was attacked through Russian, Belarus and Crimea borders

Ukraine was attacked through multiple borders, the Ukrainian state border service said early Thursday.

"At about 5:00am, the state border of Ukraine in the area with the Russian Federation and the Republic of Belarus was attacked by Russian troops supported by Belarus," the service said. 

It added that attacks are being carried out in Luhansk, Sumy, Kharkiv, Chernihiv and Zhytomyr regions — areas on the eastern and northern borders of Ukraine, reports CNN.

The attacks are targeting border units, border patrols and checkpoints using artillery, heavy equipment and small arms, the border service said.

"In addition, the attack takes place from the Autonomous Republic of Crimea side," said the service.

In recent weeks, Russia has amassed a significant number of troops, vehicles and tanks in Belarus near the border with Ukraine. During that time, the two countries have held joint military exercises across the countries, and near the Belarus-Ukrainian border.

Russian President Vladimir Putin and Belarusian President Alexander Lukashenko spoke by phone on Thursday, according to Belarusian state news agency Belta.

"At about 5:00am today, a telephone conversation took place between the Presidents of Belarus and Russia, during which Vladimir Putin informed his Belarusian counterpart about the situation on the border with Ukraine and in the Donbas," Belta cited the Belarusian presidential press service as saying.

CNN has witnessed, through a livestream video, troops atop a column of military vehicles entering Ukraine from a border crossing with Belarus.

The livestream video was taken at the Senkivka, Ukraine crossing with Veselovka, Belarus. The column was seen entering Ukraine around 6:48am local time. 

The US Department of Defense is tracking the reported incursion of troops from Belarus into Ukraine, a US defense official said Thursday.  

It was not clear if the troops were only Russian or also Belarusian, the source said.