European Commissioner for Trade Cecilia Malmström | Aris Oikonomou/AFP via Getty Images Malmström: Excluding UK from steel tariffs would question ‘the whole EU’ Trump has previously signaled interest in boosting trade ties with UK after Brexit.

EU trade chief Cecilia Malmström told U.S. President Donald Trump Friday that he should respect the EU as "a whole body" and warned against potentially singling out Britain from steel and aluminum tariffs.

"There are different rumors about ‘that could be excluded and that could be excluded,’ and it is not crystal clear what came from the president yesterday," she said at the Brussels Forum.

"But our assumption is that the EU is a whole body and that the U.S. will respect that," she added. "Otherwise that is questioning the whole EU as a project, which is quite dramatic."

The U.K. is a supplier of a specific type of steel used in some American military submarines. And Trump has previously signaled interest in boosting trade ties with the U.K. after Brexit.

The U.K. will remain a member of the European Union for another year before its planned exit from the bloc in late March 2019.

"We have of course talked to London and to the ministers there as well," Malmström said. "I think also with this it is in their interest that we act, if we have to, together. Because the U.K. has an important steel industry."