Zimbabwean security agents arrested a leader of the opposition MDC today ahead of a swearing-in ceremony for a new unity cabinet in which he was due to take a post, the party said.
The arrest did not stop the ceremony from going ahead.
But it could increase tensions between President Robert Mugabe and new Prime Minister Morgan Tsvangirai, from the MDC, after they ended months of deadlock over a power-sharing deal designed to rescue their ruined country.
The Movement for Democratic Change said in a statement that Roy Bennett, nominated by Tsvangirai as deputy minister of agriculture, had been arrested at the airport and taken to what it called a "notorious torture and interrogation base".
Police were not immediately available for comment.
Bennett has been living in exile in South Africa after fleeing the country about two years ago because police wanted to question him in connection with the discovery of an arms cache in eastern Zimbabwe.
Foreign investors and Western donors want concrete signs of stability in Zimbabwe. They have made it clear that funds will not flow to the southern African country until a democratic government is created and economic reforms are made.
Tsvangirai told the BBC that resistance to power-sharing could be expected from those who feel they have been left out or want to hold onto power at all cost.
"Of course there is residual resentment and you've got to deal with that, but to me the general thrust and momentum of the process is irreversible," Tsvangirai said.
"The underlying thing is that we have to find a solution to the country's crisis. Mugabe may be part of the problem, but he's also part of the solution."
Both sides have named party stalwarts to the cabinet rather than technocrats seen as having the expertise Zimbabwe needs to escape its crisis. Political analysts have suggested that could lead to further mismanagement.
Close Mugabe ally Emmerson Mnangagwa, touted as a potential successor to the veteran leader, was appointed defence minister. Former defence minister Sydney Sekeramayi was appointed national state security minister.
Tsvangirai picked lawyer and MDC secretary-general Tendai Biti as finance minister.
Some of the ZANU-PF members in the new cabinet have held ministerial posts since independence in 1980, when Mugabe came to power.
Sensitivities over allocation of cabinet posts, which was the main hurdle in long power-sharing talks, surfaced again at the swearing-in ceremony.
MDC ministers refused to rehearse the oath-taking ceremony, saying Mugabe had appointed two more ministers than his party had been allocated under the power-sharing agreement.
Mugabe and Tsvangirai agreed last September to share power, but the deal stalled as they haggled over the allocation of cabinet posts, stirring doubts over whether the old foes can work together.