Russian officials warned that supplying Ukraine with U.S.-made F-16 fighter jets would escalate the war as it stretches into its 15th month.

Russian Foreign Minister Sergey Lavrov made the remarks while speaking at a military base in Dushanbe, Tajikistan. 

“We must keep in mind that one of the modifications of the F-16 can ‘accommodate’ nuclear weapons,” Lavrov said Tuesday, according to Reuters. 

“If they do not understand this, then they are worthless as military strategists and planners,” the top Russian official added. 

Lavrov’s comments are similar to the one Russian Deputy Foreign Minister Alexander Grushko made last month when he told the Russian news agency TASS that Western countries will face “enormous risks” if they supply Ukraine with F-16 fighter jets. 

“We can see that Western countries continue to stick to an escalation scenario, which carries enormous risks for them. In any case, we will take it into account when making plans. We have all the necessary means to achieve our goals,” Grushko told TASS. 

President Biden informed other world leaders at the Group of Seven (G7) summit last month that the U.S. will support a joint effort to train Ukrainian pilots to use F-16s. 

Ukrainian President Volodymyr Zelensky has been pushing for months for Ukraine’s Western allies to provide the fourth-generation aircraft, a significant upgrade to the Soviet Union-era jets Ukrainian armed forces have been flying. 

Jets like the F-16 could give Kyiv a strategic edge in providing air support for Ukrainian troops, intercepting Russian missiles and drones, attacking ground targets, and building back a gutted arsenal of Soviet-era planes.

But there are still obstacles to Ukrainian forces using the advanced fighters, such as obtaining the aircraft from its Western partners and training maintenance personnel on how to keep the warplanes in working order.

Experts say it will take months, at least, before the F-16s take to the skies above Ukraine.