Mexican and Canadian officials are increasingly frustrated by tariff negotiations with the administration of U.S. President Donald Trump, with a lack of clarity over exactly what the U.S. wants making any resolution seem impossible, sources from both countries said.

After implementing across-the-board 25% tariffs on goods from Canada and Mexico earlier this week, Trump on Thursday announced a one-month reprieve for both countries on goods compliant under a North American trade pact.

The on-again, off-again tariffs and the high-level discussions surrounding them have exasperated negotiating teams, according to three Mexican officials and two Canadian sources familiar with negotiations.