Paris - France is celebrating a victorious start to the Euro 2016 football championships after winning the opening match, but a strike by Air France pilots is threatening to to disrupt travel for hundreds of thousands of fans.Police are on high alert in the southern city of Marseille, where England and Russia supporters clashed and hurled bottles at officers on Friday night, a day before their first game.Industrial unrest, fears of terrorist attacks and devastating flooding have overshadowed the build-up to the month-long tournament. Air France said it was cancelling flights on Saturday after 25 percent of the national carrier's pilots went on strike. The airline confirmed disruption due to the four-day industrial action called by pilot unions over labour reforms a day after the start of the football tournament. "Air France regrets this situation and is making every effort to minimise the inconvenience this strike action may cause to its customers." the airline said in a statement on Friday, adding that it expected to operate 80 percent of its flights schedule. It is not the first time that the airline's pilots have gone on strike. In 2014, unhappy with how the carrier was developing its low-cost unit Transavia, pilots went on a 15-day industrial action with the airline reporting losses of more than $450m. The latest strike comes after weeks of nationwide industrial actions in France that have paralysed refineries that has led to fuel shortages. RELATED: Pilots reject Air France offer to end strike Incinerators have also been blocked, leading to piles of rubbish in parts of cities including Paris and Marseille. Security fears at Euro 2016Fears of terror attacks have also overshadowed the build-up to the Euro 2016 in France, which has been under a state of emergency since attacks by Islamic State of Iraq and the Levant (ISIL) group last November killed 130 people. Around 90 000 police and private security guards are being deployed to protect players and supporters, including 13 000 in the capital alone, where soldiers could be seen patrolling with sub-machine guns.The Paris fan zone at the foot of the Eiffel Tower was only half-full on Friday, according to police, suggesting security fears had dampened the enthusiasm of some fans.