PARIS - The French prime minister informed the unions behind a crippling railway strike over pension reform Saturday that he is open to backing down on one of the most controversial proposals: raising the full pension eligibility age to 64.

Prime Minister Edouard Philippe wrote to unions one day after the French government and labor representatives engaged in talks that had seemed to end in a stalemate after more than a month of strikes and protests.

Philippe’s letter said that the plan to raise the full pension eligibility age from 62 to 64 - the unions’ major sticking point - was open to negotiation. It was the first time the French government overtly indicated room for movement on the retirement age issue. The overture could signal hope for ending the France’s longest transport strikes in decades.

However, Philippe said any compromise was contingent on first finding a way of paying for the pensions system in a country where a record number of people are over age 90.

On Saturday, protesters in Paris marched through the streets to denounce the French government’s plans.

In scenes that have become all too familiar to Parisians, demonstrators set fire to a kiosk near the Bastille square in the center of the French capital as a minority of demonstrators in the march got rowdy..

Police fired tear gas briefly as minor scuffles broke out.

Two days earlier, hundreds of thousands of protesters took to the streets nationwide to denounce the government’s pension proposals. The unions planned further actions for next week to keep up the pressure on the government.