PARIS (AP) — Paris police fired tear gas and taxi drivers lit bonfires on a major highway Tuesday amid nationwide strikes and protests over working conditions and competition from non-traditional services such as Uber.

Prime Minister Manuel Valls met with taxi drivers in an apparent attempt to defuse tensions. He condemned the drivers' violence but promised to strengthen a police crackdown on the competing taxi services the drivers are protesting. He is also forming a panel of taxi company representatives and government ministers to discuss reforms in the sector.

Tuesday's protests are the latest challenge to the Socialist government as it tries to modernize the economy and find France's place in an increasingly globalized, online marketplace.

One in five flights were canceled at Paris airports and other flights faced delays as air traffic controllers staged a walkout and taxi drivers disrupted roads. Twenty people were detained at protests around the French capital, according to Paris police, and i-Tele television reported that two people were injured at Orly Airport when a shuttle bus tried to force its way past a taxi drivers' blockade.

Some teachers and other public servants are also on strike over wages, education reforms and working conditions.

Hundreds of French taxis, joined by a few from Belgium and Spain, blocked a massive intersection leading into western Paris. Dozens of taxi drivers tried to march onto an eight-lane bypass, but police pushed them back with tear gas. Some drivers set pre-dawn bonfires, put out later by firefighters.

Traditional taxi drivers say they're suffering unfair competition from Uber, which has faced legal challenges around Europe.

Uber's lowest-cost service is banned in France and two Uber executives go on trial next month in Paris for fraud. Previous French taxi protests have also turned violent, with ambushes of Uber drivers and passengers.

Karim Asnoun, head of the CGT Taxi Union, said at Tuesday's Paris protest: "Unfortunately the governments are weak and as unemployment is pressuring them, they cede. They think they are creating jobs, whereas for every created job there is one that's destroyed."

Uber sent a message to French customers warning of potential violence, saying the goal of Tuesday's protest is "to put pressure on the government to ... limit competition." It warned that limiting app-based car services would raise costs, put drivers out of work and send customers back to the era "before apps and smartphones."

Protests were also held in other French cities. Uber drivers "vandalize professionals who are paying taxes, who respect the rules," said Rachid Boudjema, 37, president of the taxi drivers union in Marseille. He described "American cowboys" who "want to destroy our system, the system we are all attached to."

Milos Krivokapic contributed to this report.