By Kate Abnett and Philip Blenkinsop

BRUSSELS (Reuters) -Farmers set fire to piles of tyres in Brussels on Monday in a protest to demand EU action on issues ranging from cheap supermarket prices to free trade deals, as agricultural ministers met to discuss the crisis in the sector.

Riot police fired water cannon to put out flames.

Over 100 tractors were parked around the European Union institutions' headquarters, jamming parts of Brussels, a short distance from the cordoned off area where ministers were meeting.

Farmers across Europe have been protesting for weeks to demand action from policymakers on an array of pressures they say the sector is under - from cheap supermarket prices, to low-cost imports that undercut local producers, to strenuous EU environmental rules.

Local grievances vary. But Morgan Ody, General Coordinator of farming organisation La Via Campesina, said that for most farmers: "It's about income."

"It's about the fact that we are poor, and that we want to make a decent living," Ody told Reuters.

Ody, a farmer from Brittany, France, called on the EU to set up minimum support prices and exit free trade agreements that enable imports of cheaper foreign produce.

"We are not against climate policies. But we know that in order to do the transition, we need higher prices for products because it costs more to produce in an ecological way," she said.

TRADE DEALS, GREEN DEAL

Agriculture ministers were set to debate a new set of EU proposals to ease the pressure on farmers, including a reduction in farm inspections and the possibility to exempt small farms from some environmental standards.

"Farmers need to be paid for what they do... There are aspects of the Green Deal demanded of farmers that are not remunerated. That is the core of the problem," Belgian Agriculture Minister David Clarinval said as he arrived at the meeting, referring to EU environmental requirements.

In response to weeks of protests by angry farmers, the EU has already weakened some parts of its flagship Green Deal environmental policies, scrapping a goal to cut farming emissions from its 2040 climate roadmap.

The EU has also withdrawn a law to reduce pesticides and delayed a target for farmers to leave some land fallow to improve biodiversity.

"We must change a lot in the CAP, because this Green Deal and the green targets that we have are almost impossible to reach," Latvian Agriculture Minister Armands Krauze said, referring to the EU's common agricultural policy (CAP).

French Agriculture Minister Marc Fesneau added: "I'm not saying that we cannot do the (green) transition, but there is a need to take into account the reality on the ground."

Farmers' demands also include ending free trade agreements, which farmers say have led to cheaper imports from countries where producers face less stringent environmental standards than those of the EU.

A stage set up at the protest site on Monday was draped with a sign that said "stop EU Mercosur" - a reference to negotiations to conclude a trade agreement with the Mercosur group of South American countries.