Britain's involvement in Iraq will likely last "weeks and months" and has moved beyond a solely humanitarian one, the Defence Secretary said, as RAF aircraft continued to fly reconnaissance missions to aid the fight against Islamic State extremists.
Michael Fallon said the effort to protect refugees from the Islamist fanatics would not end soon as David Cameron declared that British "military prowess" would have to play a part in pushing back the jihadist threat.
The prime minister said IS posed a "clear danger" to the UK's domestic security as he made clear the push would involve military and diplomatic efforts alongside ongoing work to help refugees fleeing massacres.
But he faced accusations from senior Church of England bishops that he had no "coherent or comprehensive approach" to Islamist extremism and was failing to protect Christians from persecution.
Fallon revealed at the weekend that the RAF had now deployed the Rivet Joint surveillance aircraft alongside Tornado bombers to provide vital intelligence on IS movements across Iraq.
Kurdish peshmurga fighters - aided by US air strikes - were reported to have regained control of the strategically-important Mosul dam in a success for the anti-IS forces.
Fallon spoke to pilots and other service members during a visit to RAF Akrotiri in Cyprus, where the UK operation is based.
"There may well now be in the next few weeks and months other ways that we may need to help save life (and) protect people and we are going to need all of you again and the surveillance you are able to give us," he said.
"We want to help the new government of Iraq and Kurdish forces. We want to help them stop the advance of IS and stop them from being terrorised."
"This is not simply a humanitarian mission. We and other countries in Europe are determined to do what we can to help the government of Iraq combat this new and very extreme form of terrorism that by IS is promoting.
Troops from the 2nd Battalion Yorkshire regiment were sent in to the Kurdish capital Erbil for 24 hours to prepare the ground for a possible rescue mission by Chinook helicopters.
Cameron, who has resisted calls to recall Parliament to discuss the crisis, ruled out sending in ground troops "to fight or occupy" but insisted tough action would be required.
The IS aim of creating a "caliphate" across a swathe of the Middle East stretching close to Europe was "a clear danger" that could result in the violence spreading to the UK's streets if it was not taken on, he suggested.
"True security will only be achieved if we use all our resources - aid, diplomacy, our military prowess - to help bring about a more stable world.
"Today, when every nation is so immediately interconnected, we cannot turn a blind eye and assume that there will not be a cost for us if we do.
"The creation of an extremist caliphate in the heart of Iraq and extending into Syria is not a problem miles away from home. Nor is it a problem that should be defined by a war 10 years ago.
"It is our concern here and now. Because if we do not act to stem the onslaught of this exceptionally dangerous terrorist movement, it will only grow stronger until it can target us on the streets of Britain."
Cameron said he would shortly appoint a special representative to the Kurdistan regional government to help co-ordinate the growing assistance.
A United Nations Security Council resolution aimed at disrupting the terrorists' flow of finance and recruits - adopted unanimously - was part of that "broader political, diplomatic and security response", he said.
Cameron said he hoped for a "new start" in Iraqi politics as newly-appointed prime minister Haider Abadi seeks to form an inclusive administration that will unite behind opposition to IS.
And he promised a concerted diplomatic push to secure the support of countries such as Saudi Arabia, Qatar, the UAE, Egypt, Turkey "and even perhaps Iran" to effort to counter the extremists.
In a strongly-worded letter to the PM - sanctioned by the Archbishop of Canterbury - the Bishop of Leeds complained of a "growing silence" over the fate of the plight of persecuted Christians.
In particular he raised questions about ministers' failure to respond to calls - including through parliamentary questions - to set out what arrangements would be made to offer asylum in the UK.
It was "difficult to discern the strategic intentions" behind the Government's overall strategy for countering the extremists, he wrote. The Church internationally should be "a primary partner in addressing this complexity", he told him.
The bishop welcomed the "notable and admirable" focus on the plight of the minority Yazidi community, which has been at the centre of an international aid operation as families flee IS massacres.