Building on a two-year study that began last year, French President Francois Holland and British Prime Minister David Cameron pledged Thursday "to proceed to the next phase in 2017 to prepare for the full-fledged development of operational demonstrators of air combat drones by 2025," according to a joint statement released after a security summit in Amiens, France.

"This test program, the most advanced in Europe, will be based on a platform of multi-purpose drones that could provide the basis for future operational capacity beyond 2030," it said.

The deal is a boon to the European aerospace and defense industries that will be contracted to develop the "Future Combat Air System" project. The British and French governments had awarded BAE Systems and Dassault Aviation with the feasibility study in November 2014. Rolls-Royce and Safran have been assigned to work on propulsion systems while Selex ES and Thales were put in charge of electronics and sensors.

The British and French governments pledged to invest billions in developing a new generation of armed drones

The agreement was signed as part of a bi-annual security summit that also commemorates the upcoming centenary the Battle of the Somme in which 600,000 British and French soldiers were killed during World War I.

United against 'Brexit'

The two leaders also used the summit as a platform to argue against a British exit from the European Union. Cameron has called a June 23 referendum over the UK remaining inside the 28-nation bloc, ostensibly to fend off anti-EU critics that have challenged Cameron's leadership.

"I am convinced that the UK's membership of the EU gives us greater security and greater capacity to project power globally," Cameron said in comments released by his office before Thursday's meeting in Amiens, 120 kilometers (75 miles) north of Paris.

Joint statement on Syria

Hollande joined in criticizing Russia for attacking rebels seeking to oust Syrian President Bashar al-Assad. The leaders called on Russian and Syria to "immediately stop attacks on the moderate opposition."

The leaders urged all parties to stick to a ceasefire and stop rights violations that are "compromising peace and threatening to dramatically worsen the refugee crisis and benefit Daesh," the leaders' statement said, using another name for the "Islamic State" group, which is the target of Russian, British, French and US airstrikes in Syria.

French police secure the area as workers tear down makeshift shelters at the migrant encampment in Calais

Demolition proceeds at Calais refugee camp

For the third day, demolition workers razed makeshift shelters in the so-called Jungle migrant camp in Calais under the close watch of dozens of police officers equipped with water cannon. Calais is a magnet for people hoping to reach Britain and many have refused to leave.

Britain has agreed to contribute around 20 million euros in extra funding to boost security at the French port of Calais where thousands of migrants have camped out hoping to cross the English Channel.

In an interview with the "Financial Times," French Economy Minister Emmanuel Macron said a Brexit could spell the end of an agreement allowing Britain to conduct border controls in Calais.

"The day this relationship unravels, migrants will no longer be in Calais," Macron told the paper, echoing British government warnings that a vote to leave the European Union could lead to thousands of people arriving on England's southern shores overnight.

Brexit supporters dismissed the statement as scaremongering.

jar/sms (AFP, AP, Reuters)