French President Francois Hollande on Tuesday promised measures to help livestock and dairy farmers, who have been protesting for weeks over what they say is a squeeze on their profits by retailers and food processors.

Since the weekend tractors have blocked roads in Normandy, including the route to Mont Saint-Michel, a famous tourist site.

Farmers on Tuesday also blocked a popular grotto in Montignac in southwest France.

The spreading protest prompted Agriculture Minister Stephane le Foll to agree to meet farmers in Caen, Normandy, later on Tuesday. Farmers had been insisting on a visit from Le Foll, rather than a meeting in Paris he had proposed, as a condition for any lifting of their blockades.

They accuse food companies and supermarkets of not respecting a deal signed last month in which they agreed to raise prices paid to farmers.

"Tomorrow's cabinet will take decisions. Beyond the issue of distribution and prices, I have asked that there should be an emergency plan for French livestock and dairy producers," Hollande told reporters in Paris.

He gave no details other than to say there would be "structural measures".

French farmers face a number of challenges, from Russia's embargo on EU food imports to slowing Chinese demand and cheap competition from other EU countries, denting profit margins that are also being squeezed by supermarkets' pricing power.

A government-commissioned report looking into pricing problems in the meat industry is now due on Tuesday rather than Wednesday as originally planned.

Le Foll rejected suggestions that France's livestock sector needed to consolidate to create larger industrial-sized plants to compete better with products from other countries.

"I do not believe in that model," he said.

Improving the livelihoods of France's often very vocal livestock farmers is a major policy of Hollande's government.

France championed the industry as a priority in a reform of the EU's Common Agricultural Policy for the 2014-2020 period, steering some EU subsidies away from larger crop-based farms.

Separately, European Union Economics Commissioner Pierre Moscovici dismissed a call by France's far-right National Front for talks between Europe and the United States on a free trade zone to be suspended.

Moscovici acknowledged on BFM TV that the current pricing structure "was not balanced".

"There are margins (to make changes), these must be discovered via negotiation," he said.

French livestock farmers staged a national "night of distress" earlier this month when tyres were set on fire, roads blocked and manure dumped outside supermarkets, mainly in western France, home to a large part of the livestock industry.