A film that graphically shows how Robert Mugabe's supporters rigged Zimbabwe's election has been smuggled out of the country by a prison officer. It is believed to be the first footage of actual ballot-rigging and comes as Zimbabwe's president faces growing international pressure.

Shepherd Yuda, 36, fled the country this week with his wife and children. He said that he hoped the film, which was made for the Guardian, would help draw further attention to the violence and corruption in Zimbabwe.

Much of the footage was shot inside the country's notorious jail system. Yuda, who has worked in the prison service for 13 years, was motivated by the intensifying violence directed towards the opposition Movement for Democratic Change (MDC) and the murder, two months ago, of his uncle, a MDC activist.

Initially he intended to chronicle secretly what life was like inside Zimbabwe's jails but he found himself present when a war veteran and Mugabe supporter organised the vote-rigging by getting prison officers to fill in their postal ballots in his presence.

Using a hidden camera, Yuda filmed for six days prior to last Friday's run-off election in which Mugabe claimed victory with 90% of the vote. Morgan Tsvangirai, the MDC leader, had earlier said his party would not be participating in the run-off because of intimidation.

"I had never seen that kind of violence before," said Yuda, of the run-up to the election. "How can a government that claimed to be democratically elected kill its people, murder its people, torture its people?"

The film, made for Guardian Films, shows how Yuda and his colleagues at Harare central jail had to fill in their ballots in front of Zanu-PF activists.

Yuda also obtained footage of Zanu-PF rallies where voters were told they should pretend to be illiterate so that an official could fill in their ballot for them on behalf of Mugabe.

He was able to film the MDC's general secretary, Tendai Biti, in leg irons in jail. Biti, now on bail, faces treason charges which carry the death penalty.

Having completed filming, Yuda left Zimbabwe with his family for a new life and is now at a secret destination.

"I don't regret doing this, although it is a painful decision I have taken," he said. "We can live without the memories of seeing dead bodies in the prison, dead bodies in the street, dead bodies in my family.

"I've lost my uncle. My father was also beaten by Zanu-PF. I am praying to God: please God deal with Zanu-PF ruthlessly."

Mugabe has now been sworn in for a sixth term as Zimbabwe's president, a process which Tsvangirai described as "a complete joke". More than 130,000 voters spoiled their ballot papers in the election.

International pressure is mounting against Mugabe. It emerged yesterday that a US draft resolution to the UN will call for sanctions against Mugabe and demand that his government immediately begin talks with the MDC.

If adopted by the Security Council, the resolution would freeze the financial assets of Mugabe and 11 other Zimbabwean officials and ban them from travelling.