BRUSSELS (Reuters) - Thousands of people marched in Brussels on Sunday against a U.N. pact aimed at fostering cooperation on migration, eclipsing a smaller demonstration in support of the deal, the signing of which brought down Belgium's government last week.

Police said some 5,500 people marched in the bigger protest, organized by Flemish right wing parties in the part of the capital where main European Union institutions are located.

A separate counter-demonstration of around 1,000 people, organized by left-wing groups and non-governmental organizations, took place in the city center.

Belgian right-wing N-VA, which is the biggest party in parliament, pulled its ministers from the ruling coalition last week after Prime Minister Charles Michel refused its demand that he not sign the U.N. migration compact in Marrakesh.

Michel had secured a large parliamentary majority in favor of maintaining Belgium's support of the U.N. text, with support from the opposition socialists and greens. Critics said the N-VA's move was the opening shot in a campaign before federal elections in May.

The U.N. pact was agreed in July by all 193 U.N. members except the United States, but only 164 formally signed it at the meeting last Monday.