US President Donald Trump named Robert O'Brien as his new national security adviser, replacing John Bolton.

Speaking from the runway in Los Angeles on Wednesday, Trump said the pair had "very good chemistry".

O'Brien has worked on foreign policy across the aisle and currently heads hostage negotiations at the State Department.

He thanked the president and said it was a "privilege" to take on the role.

President Trump also stated that new "very significant sanctions onto Iran" will be announced in next 48 hours, adding that there are many options going forward, but he is not intending to use the "ultimate option" of war.

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