"In the wake of the referendum in the United Kingdom, I discussed with my counterparts in Europe and the UK the need for negotiations to take place in a smooth, pragmatic, and transparent manner," Lew stated.
The US treasury secretary made his statement in China, where G20 finance ministers and Central Bank governors met on July 23-24.
Lew noted that during the summit the ministers and bankers reiterated commitment to enhance joint efforts to combat terrorism financing.
Besides, the participants discussed the refugee problem and implementation of the Paris agreement on climate change.
The G20 is an international forum for the world's twenty biggest economies. Its participants include the United States, Russia, China, Japan, South Korea, India, Mexico and the United Kingdom, among others.