Russians Insist No Foul Play in 2010 Plane Crash That Killed Polish President Lech Kaczynski

The Russians fired back Monday at a Polish defense minister who appeared to suggest that Moscow was behind the 2010 plane crash that killed his country's president Lech Kaczynski.

Calling Defense Minister Antoni Macierewicz's remarks Sunday "irresponsible," the Russian Foreign Ministry said they were "aimed at further destabilization of the already difficult relations between our countries."

Kremlin spokesman Dmitry Peskov blasted Macierewicz's assertions as "unfounded, biased and having nothing to do with the real circumstances of this tragedy."

Related: Polish Minister Says Foul Play Behind President's Jet Crash

In Poland, opponents of the current conservative Polish government led by Kaczynski's twin brother Jaroslaw said Macierewicz was playing with fire.

"I am terrified by these words," said Rafal Trzaskowski, a former foreign minister.

Kaczynski, his wife, Poland's central bank chief and top military brass, were killed while flying to Russia for the commemoration of the Katyn Massacre, the 1940 execution of some 22,000 Polish officers by Stalin's henchmen.

While an investigation by Poland's previous government blamed pilot error, Jaroslaw Kaczynski's Law and Justice government has launched a new probe and hinted strongly that an onboard explosion could have caused the crash. It has not directly blamed Moscow directly.

"There's no doubt that what happened over Smolensk was aimed at depriving Poland of the leadership who led our nation towards independence," Macierewicz said Saturday during a conference on warfare and terrorism.

The harsh words between two historic enemies comes just months before Poland is to host a NATO summit where it will push for the alliance to station more troops on its eastern border to thwart a newly assertive Russia.

Also, in recent weeks, the current Polish government has stoked fears that the country, which has been held up as the model of democracy, might be backsliding into authoritarianism like Hungary and Slovakia.