President Donald Trump seems enamored with the idea of launching a trade war against European Union (EU), and Europe this early is warning any such war won't be pretty - especially for the United States.

Many experts are predicting Trump will soon ratchet-up tensions with the EU as part of his protectionist America First policy. This eventuality is being boosted by recent clashes over issues such as Huawei's role in 5G development. Trump wants the EU to disavow Huawei and its 5G technology, a demand the EU has refused to grant.

Some European nations such as Germany have not excluded Huawei from their national 5G network plans.

But it would be a mistake if the Trump administration decided to impose additional tariffs on European products because of such differences, said Anthony Gardner, who served as American ambassador to the European Union from 2014 to 2017.

He was asked if the differing stance between the U.S. and some European countries on Huawei could result in trade penalties.

"That would be a mistake if that is the position that Washington is going to take that is a mistake. And the fundamental reason is that when you look at our common concerns -- the U.S. and European concerns about China -- we probably agree on 90 percent," said Gardner to CNBC during an interview in Singapore.

Trump further dented the U.S.-EU relationship by saying the EU has been  "a brutal trading partner" and singled out the bloc's subsidies to Airbus for hurting the U.S. while keeping a blind eye on similar U.S. subsidies to the Boeing Company.

Gardner said he regrets that the U.S., under Trump has seemingly chosen to view the EU as a foe. He said the two economies should work even closer together, especially when it comes to tackling concerns about China's trading practices.

Gardner said both the U.S. and the EU agree China should desist from inimical practices such as forced transfer of technology from foreign firms to their Chinese partners, and restrictions the market access of foreign firms.

"We agree on 90 percent" of the issues about China, said Gardner. "What we should be doing is work with the EU more, not threatening the EU saying we're going to put tariffs," he pointed out.

At the G7 meeting in 2018, Gardner said Trump's actions in imposing steel and aluminum tariffs on the EU on spurious national security grounds were "very foolish" and a "serious attack" on the world's trading rules.

"Guns should be pointed at enemies, not as allies," he declared. He said there was is little to prevent China or any other country from blocking imports on anything, unrelated to true concerns about national security.