The European Union's executive branch, the European Commission, has hit back at what it calls "unjustified" threats of yet more tariffs from the United States, just as it closes in on implementing the much-disputed trade agreement reached last summer between Commission President Ursula von der Leyen and US President Donald Trump.

US President Donald Trump has threatened to slap higher tariffs on European goods if the EU misses a July 4 deadline to approve a trade deal with Washington.

The proposed 10 percent tariff threatens a fragile transatlantic trade truce.