LONDON - Three more European countries on Friday promised warplanes to join the US-led air armada battering Islamic State targets in Iraq, as coalition forces seek to destroy the jihadists' oil business.
Britain, Belgium and Denmark approved plans to join the war in the air, but Washington warned up to 15,000 "moderate" rebels would need to be trained and armed to beat back the militants in Syria, where they have set up their de facto capital.
The Pentagon said air strikes - which continued for a fifth day in Syria - had disrupted lucrative oil-pumping operations that have helped fund the militants, but that a final victory, perhaps years away, would need local boots on the ground.
The White House welcomed the new European countries recruited to the Iraq operation, who are expected to add a total of 19 fighter jets in the air campaign over the country.
That would free up more US air power to strike jihadist targets in Syria, where American jets are already flying with warplanes from four allied Arab countries.
Britain's House of Commons voted by 524 lawmakers to 43 to back a motion authorising air strikes in Iraq.
British Defence Secretary Michael Fallon said there would be no "immediate military action" but that it would be a "long, drawn-out campaign".
"We have to select our targets in accordance with the American and international effort that's going on in Iraq," Fallon told Sky News.
And he noted that there had been "a lot of support" for military action in Syria as well, during a sometimes heated parliamentary debate.
Ahead of the vote, Prime Minister David Cameron told lawmakers the IS group must be confronted.
"This is not a threat on the far side of the world. Left unchecked, we will face a terrorist caliphate on the shores of the Mediterranean," Cameron said.
Washington wants to build the broadest possible coalition including Sunni Arab allies to tackle IS, which has captured large areas of Syria and Iraq and declared an Islamic "caliphate".
But it has explicitly excluded Bashar al-Assad's Syrian regime in Damascus, favouring instead moderate rebel factions fighting both the government and IS extremists.
This led to criticism of the operation from Russia, whose Foreign Minister Sergei Lavrov told reporters at the United Nations that the US-led strikes are illegal unless coordinated with Syria - a Moscow ally.
Oil trade shutdown
Britain, Belgium and Denmark should join warplanes from the United States, France, Saudi Arabia, the United Arab Emirates, Bahrain and Jordan that are already hitting IS targets.
The Netherlands is also sending six F-16 jets and will provide 250 military personnel and 130 trainers for the Iraqi military, and Greece said it would send arms to Kurdish forces in Iraq.
In recent days, Washington and its allies have targeted the funding sources of what US President Barack Obama has branded a "network of death".
A US defence official, speaking to AFP on condition of anonymity on Friday, said US aircraft had launched a fresh wave of bombing raids in Syria.
The mission is now similar to US-led air raids undertaken in Iraq, with "near-continuous" combat flight operations over Syria, the official said.
The coalition has also bombed oil refineries in eastern Syria where IS jihadists extract crude for sale on the black market, according to the Syrian Observatory For Human Rights, a British-based watchdog.