The European Union is open to lowering tariffs on U.S. fertiliser imports as an offer in trade talks with the Trump administration, but will not weaken its food safety standards in pursuit of a deal,

"The European Union... has been very difficult to deal with," Trump said, adding: "Our discussions with them are going nowhere!"

Stock markets declined after the president’s early-morning threats of 25 percent import taxes on iPhones and 50 percent on goods from Europe.