Zimbabweans go to the polls Saturday to vote on a new constitution that would pave the way for elections, but many believe the army and police, not voters, may ultimately decide the country's fate.

While the referendum on the constitution is largely expected to be fair, the main event -- elections slated for July -- may be decided by the outsize influence of a handful of those close to President Robert Mugabe, 89, the country's leader for the past 33 years.

Those allies include police chief Augustine Chihuri, who reportedly told senior police officers at a retreat late last year that anyone who did not support Mugabe's party, the Zimbabwe African National Union-Patriotic Front (ZANU-PF), had no business being on the force.

Lest there be any confusion, Chihuri also denounced Mugabe's opponents, including Prime Minister Morgan Tsvangirai, as "stooges of the West".

Police officers across the country were also ordered to register as voters, and, reportedly, to vote for ZANU-PF.

Chihuri, a key Mugabe ally, is a veteran of Zimbabwe's liberation struggle. He is also Zimbabwe's longest-serving police chief since independence in 1980.

He is one of many senior security force officials in Mugabe's inner circle.

Oliver Mandipaka, a senior police officer, is reported to have thrown his hat into the ring as a ZANU-PF parliamentary candidate in Buhera, in south-east Zimbabwe.

High-ranking army officers such as Brigadier General Douglas Nyikayaramba have also publicly declared their allegiance to ZANU-PF.

In 2002 Nyikayaramba served as chief election officer of the Electoral Supervisory Commission, but by 2011 he openly described Tsvangirai -- who leads the Movement for Democratic Change (MDC), ZANU-PF's main competition -- as a security threat.

Takavafira Zhou, a political analyst from Masvingo State University, said high-ranking police and army officers' reach extended deep into the electoral process.

"The security chiefs are the ones calling the tune," said Zhou.

"Their subordinates are among the polling officers and form part of the machinery that can manipulate the vote in favour of ZANU-PF if need be, but I am surprised the MDC is turning a blind eye to all that.

"Security chiefs will determine the outcome and what happens after the outcome, and they will certainly not accept an MDC victory."

Police spokeswoman Charity Charamba was not available for comment.

Already the police force has launched a crackdown, raiding the offices of rights groups and seizing documents and communication equipment.

Activists have been detained and charged in what critics say is a campaign to silence Mugabe's critics and instil fear ahead of the July vote.

"You can already see the state security agents continue to play a significant role to ensure a ZANU-PF victory through the criminalisation of civic society on the basis of trumped-up charges," said Thabani Nyoni, director of the civic group Bulawayo Agenda.

"The whole machinery of intimidation, repression and propaganda has been reawakened and as we approach the elections, where the stakes are higher, they will intensify the campaign to silence any dissenting voices."

Essie Ncube, a political analyst based in Bulawayo, Zimbabwe's second city, said the security forces "have the potential to destabilise the capacity to have free and fair elections."

But not all observers agree.

Bassie Bangidza, from the University of Zimbabwe's department of security studies, said the military poses no threat to the vote.

"The only way they can influence the elections is by voting," Bangidza said.

Political scientist Ibbo Mandaza, head of the Harare-based Southern African Political and Economic Series (SAPES) Trust, agreed the threat posed by the security forces was exaggerated.

"If they were ever involved in influencing the vote, it was to the extent to which the political leadership has allowed them to do so," Mandaza said.