A decision by the Obama administration on providing aerial tankers is expected within days, but the United States wants a clearer explanation of French plans for its mission, including whether more forces would be committed and how the French planned to end their leading role in the military campaign.

A French official, speaking on ground rules of anonymity to describe bilateral discussions, said some officials in Washington were concerned that assigning American tanker planes to refuel French warplanes bombing Islamist militant targets in Mali might make the United States appear as a co-belligerent in the conflict. Even if that view was not supported under international law, it could be the perception across the Muslim world.

One administration official confirmed that those concerns had been discussed in Washington. “If we are seen as a co-combatant, what does that mean for U.S. facilities and personnel in the region, and what are the costs associated with that?” the official said. “We are working through these issues, but there is no lack of support for our ally.”

The French official explained that the request for American refueling aircraft was submitted only as a prudent alternative if the mission continues for longer than anticipated — or in case there is a significant military crisis requiring the immediate dispatch of additional French aircraft.