“Local authorities are committing acts of suppression by trying to seize documents of the NLD and detain or interrogate township organizers,” the National League for Democracy (NLD) said a day after the junta-drafted charter was made public.

NLD spokesman Nyan Win told Reuters least three NLD were attacked by unknown assailants as they campaigned against the constitution in Yangon, the former Burma’s biggest city.

“For this reason, it is now obvious that the forthcoming referendum cannot be free and fair,” the party’s executive committee said in a statement demanding foreign observers, including from the United Nations.

Myanmar Information Minister Kyaw Hsaw promised last month the vote would be “free and fair”, but he bluntly rejected offers of U.N. technical assistance and monitors.

The charter, dismissed by Western critics as a ploy to entrench 46 years of army rule, grants the military an automatic 25 percent of seats in parliament.

It also gives the commander-in-chief the right to suspend the constitution at will.

The regime, which tightly controls the media in the former Burma, has urged the country’s 53 million people to back the charter, a key step in the junta’s seven-point “roadmap to democracy” meant to culminate in multi-party elections in 2010.

The official New Light of Myanmar newspaper accused unnamed foreign governments of aiding the opposition to “destabilize the country” ahead of the referendum.

It said some foreign diplomats in Yangon had visited NLD headquarters to “give directives to harm the interests of the nation and the people”.

It did not name the embassies, but said their activities violated international law and should stop.

On the streets of Yangon, Buddhist monks were among those who snapped up copies of the 194-page charter selling for a $1 at private stalls and government bookstores.

“Fifty copies sold like hot cakes in less than an hour,” a roadside bookstall owner told Reuters. “I never thought our people would be so keen on the constitution”.

The junta, which sparked international outrage last September when troops crushed anti-junta protests, has ordered civil servants to vote “yes” next month and to persuade their family members to do so too.

“We have been told we will have to vote in our offices,” a government employee said. The regime has not publicly explained how the referendum will be run.

The NLD’s Nyan Win said many people would not have enough time to study the constitution.

“Most people in Yangon will get their copies only today. What about those in provinces?,” he said.