Prime Minister Shinzo Abe on Wednesday condemned U.S. President Donald Trump's reported move to impose tariffs of up to 25 percent on imported vehicles as unwarranted and offensive.

"If the U.S. slaps Japan, its ally, with tariffs like this, that would be incomprehensible and unacceptable," Abe told the head of the Democratic Party for the People, Yuichiro Tamaki, during a debate between party leaders in the Diet.

The Trump administration recently launched a Section 232 national security probe into whether vehicle and parts imports are harming the U.S.'s domestic auto industry — a step that could provide Trump with the legal basis to institute tariffs. The move followed yet another surprise announcement by the Trump administration in March that Japan, unlike Washington's other key allies and partners, wouldn't be excluded from steel and aluminium tariffs.