Police fired tear gas, stun grenades and water cannon in battles with “yellow vest” protesters around the Champs Elysees in Paris on Saturday, marking the third weekend of demonstrations across France against high living costs.

Police said 122 people had been arrested amid concerns that violent far-right and far-left groups were infiltrating the ”yellow vests” movement, a spontaneous grass-roots rebellion over the struggle of many in France to make ends meet.

Challenge to Macron

For more than two weeks, the “gilets jaunes” (yellow vests) have blocked roads in protests across France, posing one of the largest and most sustained challenges Emmanuel Macron has faced in his 18-month-old presidency.

In Paris, masked and hooded protesters picked up and hurled crowd barriers and other projectiles in running battles with police around the world famous Champs Elysees boulevard.

Six policemen and 14 protesters have been injured, Paris police said. “We are attached to dialogue, but also the respect for the law,” Edouard Philippe told reporters. Several hundred yellow vests sat down around the Tomb of the Unknown Soldier under the Arc de Triomphe at the top of the avenue, singing La Marseillaise, France’s national anthem, and chanting, “Macron Resign!”

Mr. Philippe said across France there were some 36,000 protesters and 5,500 in Paris. Police unions said there were 582 road blockages in France. Nantes airport in western France was briefly closed after protesters reached the tarmac.

The immediate trigger for the protest wave was Mr. Macron’s decision to raise tax on diesel fuel in a move to encourage the driving of less-polluting cars.