The body of a young Syrian man has been found in Poland near the border with Belarus, Polish police said on Saturday, amid mounting international tension over a migrant crisis the European Union says has been orchestrated by Minsk.

Thousands of migrants from the Middle East are sheltering in freezing conditions on the border between Belarus and EU states Poland and Lithuania, which are refusing to let them cross. Some have already died and there are fears for the safety of the rest as bitter winter conditions settle in.

“Yesterday, in the woods, near the border, near Wolka Terechowska, the body of a young Syrian man was found,” Podlaska Police said on Twitter.

The police said they had been unable to determine the cause of death at the scene.

The discovery comes amid mounting international tension over the crisis, with neighbours of Belarus warning the situation could escalate into a military conflict and U.S. President Joe Biden expressing his concern.

Belarus said on Saturday that the number of migrants arriving at a makeshift camp on the border was growing daily, and that a group of up to 100 had crossed into Polish territory.

“There’s a group (of migrants) close to the crossing point… They are indeed on Polish territory. Up to 100 people,” the RIA news agency quoted the Belarusian state border committee as saying.

The Polish Border Guard said Belarusian soldiers had torn up a section of the temporary fence erected by Poland to deter migrants during the night.

Russian President Vladimir Putin, a key ally of Belarusian President Alexander Lukashenko, said Belarus has nothing to do with the migrant crisis.

On Saturday, Polish Interior Minister Mariusz Kaminski told private broadcaster RMF FM he would meet U.S. Director of National Intelligence Avril Haines to discuss the situation next week. He said around 1,500 people were camped at the border and that this number was growing.

Poland, Austria, Lithuania, Latvia and Estonia have asked international aid organizations to organise humanitarian and medical assistance in Belarus to “avoid tragedies and prevent (a) humanitarian crisis” at the Polish border.

The Polish Border Guard said there were 219 attempts to illegally cross the border on Friday. The Lithuanian border guard says 144 migrants attempted to enter on Friday.