The United States has refused to provide air defense support for a planned European “reassurance force” in postwar Ukraine, Bloomberg reports, citing people familiar with the matter.

European allies, particularly the UK and France, had sought a firm security guarantee from the US to back a proposed “reassurance force” that would deter Russia from violating any potential ceasefire. However, discussions with US counterparts revealed that President Donald Trump is unlikely to offer the military support they had hoped for, according to sources cited by Bloomberg. 

British Prime Minister Keir Starmer had emphasized the need for a US guarantee, stating in February:

“US security guarantee is the only way to effectively deter Russia from attacking Ukraine again.”

Nonetheless, the lack of US commitment has forced Europe to adjust its approach.

Shift in deterrence planning

Despite downgraded expectations, UK and French officials hope the US will continue providing intelligence and border surveillance, Bloomberg reports. Some European officials believe Trump might act if European troops are directly targeted by Russia, but sources suggest he will not commit such guarantees in writing.

European governments have adapted their strategy, now relying on a mix of Ukrainian forces, allied training, and European troops and aircraft stationed along NATO’s eastern flank. Regular patrols in the Black Sea are also being considered part of this new framework to deter Russian aggression.

Coalition development and limitations

The coalition being led by the UK and France aims to safeguard Ukraine’s airspace, coastline, and key infrastructure using European troops positioned away from the border. However, the entire plan is contingent upon a future peace deal, which European officials view as increasingly unlikely.

While the UK and France have finalized details of the force’s deployment and operation, Bloomberg reports that the initiative remains suspended until ceasefire negotiations resume.

Of the 30 nations participating in the coalition — including non-European countries such as Canada, Australia, Japan, and New Zealand — only fifteen have so far pledged military resources like aircraft and naval vessels. Even fewer have committed troops.