WARSAW, Poland (AP) — Poland’s police said Sunday they received information about a possible plot to attack Prime Minister Donald Tusk and Defense Minister Władysław Kosiniak-Kamysz.

Poland has been on high alert following a series of school stabbings this week, as well as fears of a possible Russian hybrid attack to weaken Western support for Ukraine in its war against Moscow’s full-scale invasion.

“We take this matter extremely seriously,” said Jacek Dobrzyński, spokesperson for the minister overseeing Poland’s intelligence services. He said authorities considered there was a “high probability” the threats would be carried out.

Dobrzyński was speaking after an emergency meeting of security services, police and representatives of the Interior Ministry on Sunday. He said information about the threat first reached the state protection service, which then passed it to the police.

He gave no other information about the reported plot.

Adam Szłapka, a spokesperson for the Polish government, told Polish media Tusk learned about the threat first thing on Sunday morning. He said that, even if officials do occasionally get threats, this one was “exceptionally concerning.”

Dobrzyński said that the Polish services were receiving an increasing number of various threats with every month.

Three attacks at schools in Mazovia province in central Poland took place within four days this week, leaving one dead and many wounded, including children.

In September, Tusk warned about likely intensified hybrid attacks by Russia on NATO’s eastern flank. He said Russia was planning strikes with drones or rockets on European countries supporting Ukraine, among them Poland, with the goal of weakening Western support for Kyiv’s fight against the Russian invasion. Moscow has denied any such plans.