Barack Obama has authorised air strikes against Islamist militants in Iraq, insisting his decision was taken to prevent a "potential act of genocide."
The US president gave the green light to "limited" air strikes and emergency assistance missions in Northern Iraq, where thousands of Yazidi Iraqis have been forced to take shelter on a mountain-top refuge.
Obama said the US military will seek to help Iraqi forces, as well as assisting them in breaking the siege and in protecting the civilians trapped in the northern region of the country.
The US president also said he wanted to ensure the safety of the US personnel if they were to come under threat by Islamic State militants anywhere in the country.
"When we face a situation like we do on that mountain, with innocent people facing the prospect of violence on a horrific scale and we have a mandate to help - in this case a request from the Iraqi government - and when we have unique capabilities to act to avoid a massacre, I believe the United States cannot turn a blind eye," Obama said in a late-night statement from the White House.
"Earlier this week, one Iraqi said no-one is coming to help. Well, today America is coming to help," he continued.
Militants are closing in on Erbil, the the capital of the Kurdish semi-autonomous region in northern Iraq, a region that had enjoyed relative stability up until now but which is now under threat the jihadist group Islamic State (Isis) continues to sweep through the region.
UN officials say an estimated 200,000 refugees are seeking shelter in the north of Kurdistan, with some 50,000 Christians fleeing the town of Qaraqosh on Thursday, while other Christian towns, such Tel Askof, Tel Keif and Qaramless, have also been left almost deserted.
So far Iraqi troops have focused on defending Baghdad and the south of the country, leaving the the Kurdish peshmurga to defend minorities in the north, which has seen Yazidis, Christians and Turkmen uprooted from areas they've occupied for centuries.
"In recent days Yazidi women, men and children from the region of Sinjar have fled for their lives," said Obama.
"Thousands, perhaps tens of thousands are now hiding high up the mountain with little but the clothes on their backs, they are without food, they are without water.
"People are starving, children are dying of thirst. Meanwhile Isis forces below have called for the systematic destruction of the Yazidi people, which would constitute genocide."
Prime Minister David Cameron said it welcomed Obama's decision to proceed with a campaign of aid drops and air strikes, however the UK will not be joining the US in military action.
"I welcome President Obama's decision to accept the Iraqi government's request for help and to conduct targeted US air strikes, if necessary, to help Iraqi forces as they fight back against Isil terrorists to free the civilians trapped on Mount Sinjar," Cameron said in a statement.
"And I fully agree with the president that we should stand up for the values we believe in - the right to freedom and dignity, whatever your religious beliefs."
The effects of Obama's announcements were felt immediately by the markets, with FTSE100 losing 0.5%, Germany DAX down 1.1% and Italy FTSE MIB and Spain IBEX losing 1.2% and 1%, respectively.
The price of oil jumped on Thursday following the announcement with light crude oil
up 0.79 points to $98.45.
"As it is widely recognised that the northern area of Iraq holds the country's highest oil reserve - reportedly up to 70% - I expect that oil prices
will continue to rise if the conflict is prolonged and a return to the $108 area for Brent (WTI) might be on its way," said Jameel Ahmad, chief market analyst for FXTM.