US President Donald Trump on Thursday chose John Bolton as his new national security adviser .
Mr Bolton is a hawk who has advocated using military force against Iran and North Korea and has taken a hard line against Russia.
Mr Trump said in a tweet that Mr Bolton would replace HR McMaster, his current national security adviser. Mr Bolton, 69, who has long been a polarising figure in Washington foreign policy circles, becomes Mr Trump's third national security adviser in 14 months.
Mr Bolton joins a Trump national security team that with the planned replacement of Secretary of State Rex Tillerson by CIA chief Mike Pompeo, is increasingly populated by figures who share Mr Trump's penchant for exercising US power unilaterally.
As the State Department's top arms control official under President George W Bush, Bolton was a leading advocate of the 2003 invasion of Iraq - which was later found to have been based on bogus and exaggerated intelligence about President Saddam Hussein's weapons of mass destruction and ties to terrorism.
In recent years, as a conservative media commentator, Mr Bolton has advocated hardline positions on stopping Pyongyang from getting nuclear weapons that could threaten the United States. He has also advocated getting rid of the 2015 Iran nuclear deal, a pact Mr Trump has also heavily criticised.