(adds comments, analyst, background, Tsvangirai to campaign)
By Cris Chinaka
HARARE, May 14 (Reuters) - Zimbabwe's run-off presidential election due this month was put off on Wednesday until as late as July, prompting the opposition to say President Robert Mugabe was trying to buy time for a crackdown.
Zimbabweans voted on March 29, but results of the disputed vote were only released on May 2.
They showed opposition leader Morgan Tsvangirai beat Mugabe, but not with enough votes to avoid a run-off that should have been held within 21 days of the results.
In a special government gazette published on Wednesday, Justice Minister Patrick Chinamasa said on behalf of the Zimbabwe Electoral Commission, or ZEC:
"The period within which a second election for the office of the president is hereby extended from 21 days to 90 days from the date of announcement of results of the first poll."
That means the second round of voting for president may only take place in July -- four months after Zimbabweans first cast parliamentary and presidential ballots -- which could heighten tensions and spark further violence.
In the parliamentary vote, the ruling ZANU-PF party lost its majority to the opposition for the first time since independence from Britain in 1980. The new parliament has not yet sat.
An opposition Movement for Democratic Change (MDC) spokesman said of the delay: "This is illegal and unfair. It is part of a programme to give Mugabe and ZANU-PF time to torment and continue a campaign of violence on the MDC."
Lovemore Madhuku, constitutional lawyer and head of the National Constitutional Assembly pressure group fighting for a new constitution, said the delay was unlawful.
"It's unlawful under the Electoral Act. ... The Act automatically sets the run-off date, from the date of the first round. What they have done is ridiculous and fundamentally flawed. It's political mischief and it's very sad that ZEC is allowing itself to be used to ambush the opposition," he said.
Independent election observer group Zimbabwe Election Support Network also said any run-off held after the stipulated 21 days would be in breach of the law. It noted conditions were not conducive to a free and fair poll.
The MDC accuses ZANU-PF of waging a campaign of violence and intimidation against its supporters as part of efforts to rig the vote. It says 32 of its supporters have been killed in the aftermath of the elections.
The government denies the accusations.
The southern African SADC grouping which will monitor the polls said earlier on Wednesday that the political environment was not yet suited for a secure and fair run-off.
"We can't say the playing ground is safe or will be fair, but we are there to create a conducive environment for everybody to be confident," SADC Executive Secretary Tomaz Salomao told Reuters in neighbouring Mozambique.
SADC observed the first round of the vote in March and Salomao said it planned to send a bigger team to the run-off. Regional states are concerned turmoil and instability in Zimbabwe could spill over and take their toll on them too.
An economic meltdown in Zimbabwe has triggered inflation of 165,000 percent, 80 percent unemployment, chronic food and fuel shortages and a flood of refugees to neighbouring states.
Tsvangirai had initially said he would only contest the run-off if international observers had full access, but told Reuters on Tuesday he would be satisfied if just SADC monitors attended.
The MDC said on Wednesday he would return home for the first time in a month to start campaigning for the run-off on Sunday.
SADC had sent 120 observers to the first round, and Salomao said it planned to send at least 200 observers to the run-off and possibly more than 300. But he ruled out sending peacekeepers as requested by Tsvangirai. (Additional reporting by MacDonald Dzirutwe and Cris Chinaka, and Charles Mangwiro in Maputo; Writing by Marius Bosch; Editing by Richard Meares) (For full Reuters Africa coverage and to have your say on the top issues, visit: africa.reuters.com/)