Two days ago, Polish security officials arrested two men on suspicion of espionage for Russia. Given the current climate of high tension on Poland's eastern frontier, thanks to Russia's war on Ukraine, the timing of this arrest is important. For NATO, too, the stakes are high.

Polish officials have been tight-lipped about the case and the names of those under arrest have not been released. However, we know that one man is a colonel in the Polish military, assigned to the Ministry of Defense (MoD) in Warsaw, while the other is an attorney in Poland's capital, a dual Polish-Russian national who works on economic matters.

Although the men were arrested on the same day, their cases were investigated independently; it is not yet clear whether they are linked. Poland's Internal Security Agency (ABW) has said little about this affair, officially not citing which country the men are believed to have spied for, although an ABW spokesman stated coyly, "I think you can probably guess which country." Yesterday, however, a member of the parliamentary commission for the security services revealed that the men had been secretly working for Moscow, specifically for Russian military intelligence (GRU).

Anytime a colonel in the defense ministry is suspected of espionage is a moment to worry -- Polish counterintelligencers will be very busy in the weeks ahead trying to assess the damage -- but to make matters worse, it has been revealed that the officer had access to NATO secrets, so the Atlantic Alliance must now assume the worst. Polish counterintelligence has a long history of tangling with GRU, and the results have not always been edifying for Warsaw, as I've previously explained, because the Russians excel at espionage.

We can take the Polish MoD's word that the charges facing these men are "very serious" indeed. Warsaw has promised to reveal more details of this case in a few days, and I'll be reporting on that and giving my analysis. Watch this space.