The USA rejected the proposal for the deployment of American military equipment maintenance companies (contractors) in Ukraine cfor the maintenance of Western military equipment, including F-16 fighter jets.

A Wall Street Journal report says the Biden administration chose not to move forward with the proposal due to security concerns after Ukraine lost the first F-16 fighter jet it received from Western allies earlier this month.

On August 28, the Ukrainian General Staff confirmed that the F-26 had crashed during combat operations against Russian forces.

Debate over sending American civilians to a country fighting Russian forces to help maintain Western equipment has been around since the early days of the war, but has recently become more heated with the long-awaited arrival of F-16s in Ukraine. The first six of the 80 F-16s arrived in Ukraine in late July.

The National Security Council considered a proposal to send maintenance companies to Ukraine for F-16 fighter jets and other military weapons, but intelligence agencies deemed it too risky for now, officials familiar with the discussion said, the Wall Street Journal reports. Instead, they hope that European countries will take more—and perhaps all—responsibility for maintaining the F-16s.

“Intelligence agencies have raised concerns about the prospect of Russia targeting American contractors in Ukraine,” a US official said.

The administration has not ruled out sending U.S. military maintenance companies to Ukraine in the future, but they are not expected to go there anytime soon.

“That’s something we’re looking at, but we haven’t made any decisions,” Sean Savett, the National Security Council’s principal spokesman, said in a statement about the proposal to send U.S. contractors to Ukraine.

On Monday, Ukraine lost its first F-16 during a Russian attack. Ukrainian and US officials have not released the cause of the crash, which killed a prominent pilot, and the investigation is ongoing.

The American-designed aircraft remains one of the US Air Force’s most iconic combat aircraft and requires highly specialized maintenance and other support, including hours of service for every hour of flight. Dozens of support personnel typically work for each fighter.

While the Pentagon has said it hopes the Ukrainians can maintain the F-16s, all countries, including the US, rely to some extent on private companies and their personnel to help support the complex fighters.

Maintenance of the warplanes could prove critical to Ukraine’s defense on its soil. Without civilian contractors to maintain the planes—such as repairing and replacing parts—Ukraine will struggle to keep Western-supplied planes operational.

The Biden administration’s reluctance to send U.S. contractors to Ukraine to support U.S. and other Western equipment reflects the larger debate over U.S. involvement in the war there.