Donald Trump’s new national security adviser has said America should “prepare for war” to secure peace amid signs a more hardline US foreign policy is emerging.

John Bolton, the former US ambassador to the United Nations, made the comment just hours after being appointed to the role via a tweet from Mr Trump.

"The surest way to avoid conflict is to have a strong military capability,” Mr Bolton told Sky News.

“As the ancient Romans used to say: Si vis pacem, para bellum - if you want peace, prepare for war."

Mr Bolton will replace HR McMaster, the retiring general, on April 9 to become Mr Trump’s third national security adviser in 14 months.

The 69-year-old, who served in the UN under George W Bush, is known for his hawkish foreign policy views and no-nonsense approach to diplomacy.