Brussels, June 27 -- Acting U.S. Defense Secretary Mark Esper made it clear to Turkey on Wednesday that it will face economic sanctions if it goes ahead with the purchase of a Russian missile defense system, as the standoff between the two NATO allies dragged on.

Esper met with Turkish Defense Minister Hulusi Akar during a NATO meeting, delivering a familiar U.S. message: If Turkey buys the Russian S-400 system, it will not be allowed to buy the high-tech F-35 fighter jet. The meeting, however, ended with no discernable results.

A senior defense official traveling with Esper said the two men had a frank and candid discussion, but the meeting resulted in no movement or change of position on either side. The official spoke on condition of...