NATO allies consider it unlikely that Ukrainian forces will be able to hold Russian territory, even if it takes weeks for Moscow to force them out of Kursk Region, a Western official familiar with Kiev’s planning of last week’s incursion has told Bloomberg.

Elements of six Ukrainian brigades invaded Kursk Region in the morning of August 6, taking over several border villages. Moscow has introduced a state of emergency and launched a counter-terrorist operation in the region, which borders Ukraine’s Sumy. The Russian Defense Ministry later said that the Ukrainian advance had been halted, estimating enemy losses at up to 2,000 service members and more than 200 armored vehicles.

According to the unnamed NATO official, cited by Bloomberg on Tuesday, the incursion was “at least crucial to show that Kiev can challenge the Kremlin.” 

With Ukraine’s military on the defensive, a cross-border attack had been “weighed for some time” before the incursion, the Western official said. Ukraine had reportedly been weighing several possibilities for an attack aimed at putting Russia on the backfoot.

“While President Joe Biden’s administration and the European Union have given their blessing as the first military presence on Russian soil since World War II unfolds, NATO allies have so far withheld judgment,” Bloomberg wrote.

Kiev officials did not share specific information on the cross-border attack until it was well underway, according to an unnamed Western intelligence official.

Meanwhile, Deputy Pentagon Press Secretary Sabrina Singh described the attack as “consistent” with Washington’s policy on Ukraine’s use of American-supplied weapons to defend itself. The EU has also called the operation legitimate defense.

Ukrainian troops interviewed by Western outlets have admitted that the goal of the incursion was to capture some territory that could be traded with Russia in possible peace talks and to relieve pressure on the Donbass front. Moscow has since ruled out any negotiations with Kiev, while Russian troops have accelerated their advance. 

Former Russian President Dmitry Medvedev warned on Tuesday the Ukrainian government will face “ramifications” for attacking the country.