"Last time I checked he's an American. I can work with an American," Mattis told reporters.

The retired Marine general said he had never met Bolton before, but expected to get together with him soon at the Pentagon.

A former US ambassador to the United Nations and Fox News contributor, Bolton is known for his vehement opposition to the Iran nuclear deal and defense of a US first strike against North Korea.

Mattis has stressed diplomacy in dealing with both countries, and has argued against scrapping the 2015 nuclear deal with Iran.

Asked whether he could work with Bolton, Mattis said he had "no reservations, no concerns at all."

"I hope that there's some different world views, that's the normal thing you want unless you want group think," he said.