British Prime Minister David Cameron on Friday expressed his deep concern about the situation in Iraq and welcomed US President Barack Obama's decision to authorise air strikes against extremists.
But a spokesman for Cameron's Downing Street office said Britain, which joined the US-led invasion of Iraq in 2003, was not planning its own military intervention.
"I am extremely concerned by the appalling situation in Iraq and the desperate situation facing hundreds of thousands of Iraqis," Cameron said in a statement.
"And I utterly condemn the barbaric attacks being waged by ISIL (ISIS, now Islamic State) terrorists across the region."
He added: "I welcome President Obama's decision to accept the Iraqi government's request for help and to conduct targeted US airstrikes, if necessary, to help Iraqi forces as they fight back against ISIL terrorists to free the civilians trapped on Mount Sinjar.
"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."
However, a Downing Street spokeswoman said: "We are not planning a military intervention."
Cameron said he was especially concerned for members of the minority Yazidi community who fled Sunni extremist fighters and are now trapped on Mount Sinjar.
"They fear slaughter if they descend back down the slopes but face starvation and dehydration if they remain on the mountain," he said.
"The world must help them in their hour of desperate need."
He said officials had been tasked with establishing what help Britain can provide, including to civilians requiring food, water and shelter in the Sinjar area.
Defence Secretary Michael Fallon will chair a meeting Friday of the government's emergency Cobra committee on the situation in Iraq.
On Thursday, Obama ordered US warplanes back into the skies over Iraq to drop food to refugees and if necessary launch air strikes to halt what he said was a potential "genocide."