Elliot Pfebve, a member of the National Executive Committee of the Movement for Democratic Change (MDC) said his brother, Matthew, 47, was murdered late on Monday by a mob of war veterans and supporters of the ruling Zanu-PF party.
The Commonwealth action group, which monitors human rights in member-states, said Secretary-General Don McKinnon would relay their concerns to President Robert Mugabe later this month.
After a meeting in London, the eight foreign ministers who make up the group also decided to send a substantial team of monitors to scrutinise the forthcoming general elections to ensure that both the campaign and the conduct of the poll are free and fair.
New death
Their decision came as it was confirmed that supporters of President Mugabe's ruling party Zanu-PF had beaten another opposition supporter to death.
Elliot Pfebve, a member of the National Executive Committee of the Movement for Democratic Change (MDC) said his brother, Matthew, 47, was murdered late on Monday by a mob of war veterans and supporters of the ruling Zanu-PF party.
Mr Pfebve, a candidate in elections expected in June, said his father was badly beaten in the same attack but made his way home. Three other people were released unhurt.
The killing happened in a village near the eastern border with Mozambique.
At least 15 people including farm workers, opposition supporters and two white farmers have been killed in escalating pre-election violence.
Commonwealth condemnation
The London meeting was the first by the Commonwealth ministerial action group since the Zimbabwe crisis blew up.
UK Foreign Secretary, Robin Cook, set the tone for the meeting by saying the whole Commonwealth condemned the climate of intimidation prevailing in Zimbabwe.
He ruled out economic sanctions or suspension from the Commonwealth, but hinted that could change if President Mugabe failed to hold elections.
Mugabe meeting
Meanwhile in Harare, crowds of supporters turned out to greet President Mugabe as he arrived at a cabinet meeting.
The Zimbabwean Government has not disclosed what was discussed at its cabinet meeting, though land reform was expected to be high on the agenda.
There was no statement afterwards about a date for the delayed elections.
Mr Mugabe has indicated recently that he will invoke presidential powers to allow land seizures to go ahead without compensation for the present owners.
Government supporters also surrounded the court building in Harare where war veterans' leader Chenjerai Hunzvi is facing fraud charges.
He is also accused of stealing money from a compensation fund for war victims, and faces contempt of court charges over the land invasions.
The proceedings were delayed for two hours as the prosecution complained of a siege atmosphere.
Veterans pushed at the gates outside the court building, singing songs and chanting Dr Hunzvi's name.
In a separate case, Dr Hunzvi is due in court again on Wednesday to explain what steps he had against farm invasions, which courts have declared illegal.
He will be sentenced for contempt of court on Friday if his explanation fails to satisfy the court.