US President Donald Trump in his address at the White House, Washington, DC, on February 15, 2019 (Photo: AFP/VNA)

The warning came after the European Parliament the same day refused to back new trade talks with Washington, dealing an unexpected blow to efforts to avert a trade war.

Trump told reporters at the White House that the EU treats the US unfairly and Washington might slap import tariffs on a lot of their products.

By a vote of 223 to 198, the EP rejected trade talks with the US. The EP only has an advisory role with regard to the EU's negotiating mandate, but will have the final say once an agreement has been concluded.