Trump names Robert O’Brien as new national security adviser

US President Donald Trump named Robert O'Brien as new national security adviser to replace John Bolton.

"I am pleased to announce that I will name Robert C. O'Brien, currently serving as the very successful Special Presidential Envoy for Hostage Affairs at the State Department, as our new National Security Advisor. I have worked long & hard with Robert. He will do a great job!" Trump tweeted.

He is Trump's fourth national security adviser of his presidency.

As top adviser on national security, O'Brien will be tasked with tackling everything from immigration policy to heightened tensions with Iran.

The announcement came a week after Trump fired John Bolton over disagreements on Iran and other issues.

O'Brien follows Bolton, HR McMaster and Michael Flynn in the role, which does not require confirmation by Congress.

He has served as a major in the US Army Reserve. Former President Bush appointed him in 2005 to serve as a representative to the UN general assembly.

Trump personally dispatched O'Brien to help free US rapper A$AP Rocky from Swedish prison earlier this year. The hostage negotiator interviewed for the post with the President and acting chief of staff Mick Mulvaney last week.

O'Brien enjoyed support from Secretary of State Mike Pompeo, who is now the most influential national security voice in the administration.