The British air force killed three Islamic State militants in Syria, including two Britons, in the first such attack last month, Prime Minister David Cameron said Monday.
Calling the August 21 drone strike "an act of self-defense," Cameron said there was "clear evidence of the individuals in question planning and directing armed attacks against the UK."
Reyaad Khan and two others, including a second British citizen, were killed while traveling in a vehicle near the de facto Islamic State capital of Raqqa, Syria, Cameron told parliament.
While Britain participates in anti-Islamic State strikes in Iraq and uses unmanned aircraft to gather intelligence in Syria, the Royal Air Force had not targeted Islamic State militants in Syria until the August strike.
An estimated 500-600 Britons have traveled to fight with the Islamic State group alongside thousands of other foreigners as the militant group forges what it calls a "caliphate" across parts of Iraq and Syria.
To that end, the Britain-based Syrian Observatory for Human Rights on Monday said Islamic State fighters seized the last major oil field held by the Syrian government, Jazal, in the country's central desert.
Like Britain, French forces are also ramping up their anti-Islamic State actions in Syria. President Francois Hollande said that France on Tuesday will begin surveillance flights over Syria ahead of possibly joining the U.S.-led coalition of countries conducting airstrikes against Islamic State militants there.
French warplanes have been taking part in airstrikes targeting the militants in Iraq, but would be the first Western country other than the U.S. to participate in bombing targets in Syria.
"I have asked the Defense Ministry that from tomorrow surveillance flights can be launched over Syria, allowing us to plan airstrikes against Daesh," Hollande said, using an acronym for the Islamic State group.
In a wide-ranging press conference, Hollande said the flights aimed to find out what actions the Islamic State group was preparing against France and its allies — and against the Syrian population. But he said it is "inconsequential and unrealistic to put French ground in Syria, where government troops, rebel fighters, al-Qaida-linked forces and Islamic State militants are all battling for territory.
The French president spoke as thousands of Syrians and other refugee seekers continued their march toward Austria and Germany, after having crossed the Mediterranean Sea to safety.
In addition to the U.S. and France, those participating in airstrikes in Iraq include Australia, Britain, Canada, Denmark, Jordan and the Netherlands. In Syria, forces from Bahrain, Canada, Jordan, Saudi Arabia, Turkey and the United Arab Emirates have joined U.S. warplanes in bombing militant targets.
The U.S.-led coalition continued to target IS positions overnight, with four airstrikes in Syria and 11 in Iraq. On the ground, Iraqi troops and militias continue to battle Islamic State fighters for territory.
The possible expansion of the air effort in Syria follows a new development in the campaign in Iraq, where the country's own F-16 jets provided by the United States carried out their first airstrikes targeting the Islamic State group.
"Definitely they will have a positive impact in the battles in the future," Iraqi Defense Minister Khaled al-Obaidi said.
Al-Obaidi escaped a sniper attack unharmed as he traveled in a convoy on Monday. It is unclear if the minister was the target of the attack.
One of the minister's guards was wounded by the gunfire, according to an official statement.
Al-Obaidi was returning to Baghdad after visiting troops near Beiji, home to the country's largest oil refinery and a key IS target between the capital and the militant stronghold of Mosul.
Iraqi ground troops backed by militia fighters have made some progress in regaining territory, but the militants still control much of the seized territory, including several of Iraq's biggest cities.
Lisa Bryant contributed to this report from Paris.