Justice Rosa Weber's ruling on Friday came after an opposition political party, the Sustainability Network, challenged the constitutionality of Bolsonaro's decision.

His order, signed on Tuesday, was "an abuse of regulatory power" and "contravened the spirit" of a 2003 disarmament statute that prohibited the carrying of weapons in public, according to a copy of the court documents provided to journalists.

Meanwhile, documents circulating in Congress on Friday accused Bolsonaro of "going beyond" his presidential powers and described the decree as "illegal" after he gave those in a range of professions -- including politicians, journalists and truckers -- the right to carry guns, O Globo newspaper said Saturday.

Bolsonaro, a former army captain, has defended the decree as honoring the result of a 2005 referendum in which nearly 64 percent of Brazilians rejected a law that included, among other things, a total ban on the sale of firearms.

But experts warn the loosening of restrictions will fuel gun violence in a country which already has one of the highest homicide rates in the world.

Brazil recorded 64,000 murders in 2017 -- a rate of almost 31 per 100,000 inhabitants, or three times higher than the level the United Nations classifies as endemic violence.

Faced with growing opposition to the decree, Bolsonaro said Friday: "If it is unconstitutional, it must cease to exist."

But he later insisted it was not.

The decree allows licensed gun owners to buy up to 5,000 rounds of ammunition a year, depending on the type of weapon, compared with the current limit of 50, as well as own up to four firearms, according to the Igarape Institute think tank in Rio de Janeiro.

Bolsonaro, whose tough-on-crime rhetoric helped get him elected last year, has long spoken in favor of allowing people to carry guns on the streets. But that requires the support of Congress to change the law.

Critics argue his decree breaches the constitution because it creates a new law, rather than modifying an existing one.