Photo: Nyarai Mudimu/IPS

Prominent Zimbabwean human rights lawyer Beatrice Mtetwa was arrested for allegedly obstructing the course of justice. She is pictured here existing a police van as she arrived at the Harare Magistrate’s Court on Mar. 20.

Aides to the Zimbabwean prime minister have been arrested on unknown charges. The news came as vote counting was under way in a constitutional referendum.

The three senior aides to Prime Minister Tsvangirai were arrested on Sunday. Later, Alex Magaisa, another of Tsvangirai's advisors, told the AFP news agency that police gave no reason for the arrests.

"They raided the house of the principal director responsible for research and development in the PM's office," said Alex Magaisa, an advisor to Tsvangirai. "He was arrested as well as his two subordinates. We don't know the charges, but they picked up computers and a camera."

Beatrice Mtetwa, a leading human rights lawyer, was also detained.

The DPA news agency quoted the occupational organization Zimbabwe Lawyers for Human Rights as saying Mtetwa had been arrested "on allegations of obstructing ... the course of justice," after providing legal assistance to one of the Tsvangirai's aides who was arrested.

The arrests came a day after Zimbabweans went to the polls to vote on the country's new constitution.

Low turnout in constitution vote

Zimbabwe's electoral commission announced on Sunday that only around a third of the six million eligible voters had cast their ballots in Saturday's referendum.

"Over two million Zimbabweans exercised their right to vote," Rita Makarau, the head of the Zimbabwe Electoral Commission, said. Makarau also said that voting largely went smoothly "with few incidents" reported.

Officials with Prime Minister Morgan Tsvangirai's Movement for Democratic Change (MDC) said partial results indicated that around 90 percent of those who did turn out voted to support the new constitution, which had been endorsed both by the MDC and President Robert Mugabe.

The new constitution would give more power to Zimbabwe's parliament and introduce limits on presidential terms. It is also meant to pave the way for a general election to be held in July.

However, the change would not prevent Mugabe himself from running again - in fact it would not force the now 89-year-old president to leave office for another decade.

Full official results were to be announced within five days of the vote.