President Trump said Friday that he would temporarily hold off on designating Mexican drug cartels as terrorist organizations, saying he was doing so at the request of the president of Mexico, Andrés Manuel López Obrador.

“All necessary work has been completed to declare Mexican Cartels terrorist organizations,” Mr. Trump wrote on Twitter. “Statutorily we are ready to do so.”

However, at the request of Mr. López Obrador, “a man who I like and respect, and has worked so well with us,” Mr. Trump wrote, he was temporarily holding off on the designation and stepping up “joint efforts to deal decisively with these vicious and ever-growing organizations!”

Mr. Trump did not make clear how long he was prepared to delay the designation or what precisely the Mexican president had requested.