Polish Foreign Minister Waszczykowski in Warsaw. Thomson Reuters

Polish Foreign Minister Witold Waszczykowski said Friday that Russia might respond to the US strike in Syria by escalating fighting in war-torn eastern Ukraine.

"Now everyone is waiting for the reaction from Russia. Either it will react in Syria or, as some say, unfortunately, in Ukraine," Waszczykowski said on Polish TV.

"There is a certain danger here, because Russia's policy is unpredictable and in some cases even unreasonable. No doubt, there will be some answer. The only question is where."

On April 7, the US fired more than 50 cruise missiles at a Syrian airfield in response to Syrian President Bashar Assad's use of chemical weapons on civilians.

"Despite the strength of the enemy’s army the Ukrainians do not fear Russia and are ready to defend every inch of their land," Ukrainian Minister of Defense Stepan Poltorak told US congressmen on Thursday.

At least two Ukrainian soldiers have been killed and 22 wounded since the US struck Syria on April 7.

Casualties have decreased this month — compared to 30 Ukrainian soldiers killed and 198 wounded in March — because of a new ceasefire announced on April 1.

Ukrainian government map of war in eastern Ukraine. National Security and Defense Council of Ukraine

Still, Russia has consistently attempted to exert its influence and undermine stability in Ukraine and much of eastern Europe.

In January, Estonia arrested a Russian citizen on suspicion of spying. Two more Russians were also arrested last year and were found guilty of spying.

Montenegro charged two Russians on Thursday with terrorism for their alleged involvement in an attempted coup last year in the country's capital, Podgorica.

On Wednesday, President Donald Trump declared that US-Russia ties "maybe at an all-time low." After meeting with Russian President Vladimir Putin on Wednesday in Moscow, US Secretary of State Rex Tillerson struck a similar tone. Putin likewise said Wednesday that Russian-American relations have "degraded."

US Secretary of State Rex Tillerson, right, and Russian President Vladimir Putin. Reuters/Maxim Shemetov

"Until full progress is made under the Minsk Accords, the situation in Ukraine will remain an obstacle to improvement in relations between the US and Russia," Tillerson said on Wednesday after meeting with Russian Foreign Minister Sergei Lavrov.

However, Tillerson also asked European diplomats on Tuesday, "Why should US taxpayers be interested in Ukraine?"

In the last year, the US and NATO have deployed thousands of soldiers to Poland, Ukraine, and other Eastern European countries to help train Baltic soldiers and monitor NATO's eastern flank.

And on Friday, the US Air Force said that a handful of F-35s would be sent to Europe as part of a "long-planned" deployment aimed at deterring Russian aggression.