YANGON (AFP) - Rights groups on Thursday gave a lukewarm welcome to tweaks to a harsh protest law in Myanmar, criticising the authorities for keeping powers to control demonstrations.

The amendments to the 2011 law to allow authorised peaceful protests were signed by President Thein Sein on Tuesday, as he seeks to show his reform-minded administration is tolerant of some forms of dissent.

Protests were rare under the military regime that ruled the country with iron-fist, jailed dissidents and brutally cracked down on pro-democracy rallies in 1988 and 2007.

The revised law halves the jail terms for those who breach the peace at rallies to a year, while people who protest without permission face six months in jail, again half the previous tariff.

Demonstrators still need to inform the township authorities five days in advance with details of where they will protest and even the slogans they will chant, according to a copy of the bill posted on the President's Office website.

Local police also retain the right disband rallies if they are found to have breached their conditions.

"It is still a flawed law that does not accord with international standards," said Mr David Mathieson of Human Rights Watch.

The amendments do "not change the wide latitude local authorities have to thwart peaceful assembly" he said, adding more than 100 people have been sentenced for breaching the law, while 70 more face charges linked to it.

Local rights campaigners said protests would still be cramped by the revisions.

"I don't see this as a positive step for us. They make the process of getting permission very hard," said Ms May Sabe Phyu, of the Gender Equality Network.

She was charged under the protest law in September last year for leading a protest against conflict in Kachin state.

"We always want to respect the law... but sometimes getting approval is really complicated and beyond our understanding," she said, adding the complicated conditions may effectively "set people up for arrest".

Authorised and unauthorised protests have billowed out across the country since the end of outright military rule, as people test the boundaries of new freedom after decades of junta rule.