Trump announces Robert O'Brien as new national security adviser to replace John Bolton

Mr O'Brien is joining White House just as tensions with Iran have flared over attack on Saudi Arabian oil attacks

(AP)

Donald Trump has named Robert O'Brien as his new national security adviser to replace John Bolton, who was fired last week.

Mr O'Brien was previously the special presidential envoy for hostage affairs. Mr Trump tweeted: "I have worked long & hard with Robert. He will do a great job!"

The former hostage affairs envoy would step into the White House role at a particularly sensitive time, with Mr Trump announcing increased sanctions on Iran Wednesday morning after an attack on Saudi oil facilities over the weekend.

Since that attack, Mr Trump has appeared to preview a potentially strong response, as American officials have blamed Iran for the attack. Even so, Mr Trump has faced calls for stronger action than sanctions from some in his party, including senator Lindsay Graham, who said on Wednesday morning that he believed further action would be necessary.

It appears likely that Mr O'Brien's predecessor, who regularly called for military intervention overseas, would have called for tougher action as well, and it remains to be seen how the incoming national security adviser might handle the situation.

Mr O'Brien is a known face in some Washington circles, having served in various capacities during the administration of George W Bush. Later, Mr O'Brien served as a foreign policy adviser for former Republican nominee Mitt Romney, and for former Wisconsin governor Scott Walker — who notably dropped out months before the Iowa caucuses in 2016.

During the Trump administration, Mr O'Brien was once rumoured to be under consideration to become secretary of the Navy, before being appointed as special envoy for hostage affairs. In that capacity, Mr O'Brien took on an unusual case at the behest of the president, and travelled to Sweden to oversee an assault case filed against American rapper A$AP Rocky there.

Mr Trump had become particularly interested in the case, tweeting out support and calls for his release. Rocky was found guilty of assault, but did not face any prison time.