Tusk made the comments during a meeting with Bulgarian Prime Minister Rumen Radev, saying the attacks took place while the two leaders were holding talks.
"Again, we had to evacuate the border crossings at Hrubieszów and Dorohusk; you can imagine the losses and nerves this causes," Tusk said.
He said the situation required Poland to act consistently, cooperate with Ukraine and warn its European partners that the coming weeks and months could be difficult.
"This situation requires us to act very consistently here in Poland, to cooperate with Ukraine, but also to warn Europe and our European partners that this is a really difficult time and that we need to prepare well for the coming weeks and months," Tusk said.
He added that "there is currently not the slightest sign of goodwill" from Russian President Vladimir Putin and Moscow.
Tusk said he also told Radev about repeated acts of sabotage and other unusual incidents in Poland that have caused serious problems for railway infrastructure.
Poland's Government Centre for Security (RCB) issued an alert on Thursday morning for the southeastern provinces of Lubelskie and Podkarpackie because of Russian air attacks on Ukraine.
It also said Polish fighter jets had been scrambled as a precaution.
Before 8 a.m., authorities said the Ukrainian air attack had ended and Polish military aviation operations had been completed.
Later, the Operational Command of the Armed Forces said Polish military aircraft had again been operating in Polish airspace in response to further Russian air strikes on Ukraine.
Tusk also referred to a fire at a ground-based Starlink station near the town of Grójec in the central Mazowieckie province, on Wednesday evening.
He said he did not like to determine "without 100-percent certainty" whether an incident was sabotage or an accident, but added: "It doesn't look good."
Deputy Prime Minister and Digital Affairs Minister Krzysztof Gawkowski said earlier that there were strong indications that the fire had been a deliberate attempt to disrupt the station, which he described as an internet hub that also helps ensure the security of internet services in Ukraine.
Gawkowski said the station is operated by Exatel, a state-owned telecommunications company that provides internet and data transmission services to customers in Poland and Ukraine.
Interior Minister Marcin Kierwiński said on Thursday that the circumstances of the fire would be thoroughly investigated by the State Fire Service, police and prosecutors.
"But it is difficult to imagine that in cases like this, they are coincidences. Let the police do their work calmly," Kierwiński said.
He also said Russia had clearly entered a new phase of its hybrid war with Europe.
Tusk warned last Thursday that Russia could carry out what he called "accidental" drone or missile strikes on NATO countries supporting Ukraine, including Poland, as he predicted an intensification of Russian air attacks on Ukraine, including in areas near the Polish border.
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Source: IAR/PAP