The Botswana government summoned Zimbabwe's ambassador to Gaborone on Friday to express alarm over the detention of opposition leaders in the build-up to a 27 June election, the foreign ministry said.

Foreign Minister Phandu Sekelemani told Ambassador Thomas Mandigora that Thursday's detention of opposition leader Morgan Tsvangirai while he was campaigning and the arrest of his party's number two Tendai Biti on a treason charge were "unacceptable" and undermined the prospects of the poll being fair.

"Botswana is alarmed by these arrests and detentions as they disrupt electoral activities of key players and intimidate the electorate, thus undermining the process of holding a free, fair and democratic election," Sekelemani said in a statement.

"We are deeply disturbed by this unfolding situation of politically motivated arrests and intolerance which pose a serious threat to an outcome that reflects the will of the people of Zimbabwe," the minister added.

Botswana, which borders western Zimbabwe, is one of the richest countries in Africa. It has been one the few governments in a 14-nation regional bloc known as SADC to speak out over Robert Mugabe regime's treatment of the opposition.

Botswana President Ian Khama played host to Movement for Democratic Change (MDC) leader Tsvangirai for several weeks after the first round of elections in March, much to the annoyance of Mugabe.

Sekelemani said the detentions of the MDC leaders ahead of the 27 June run-off poll was "unacceptable and deserve condemnation.

"We therefore call upon the government of Zimbabwe to fully assume its responsibilities by putting an end to these acts of political harassment and intimidation to avoid a further deterioration of the situation in that country," he said.

Botswana's willingness to speak out against Mugabe is in stark contrast to that of his giant neighbour South Africa whose President Thabo Mbeki is Sadc's chief mediator between the Zimbabwe opposition and ruling party.

Briefing reporters in Pretoria on Friday, South Africa's deputy foreign minister Aziz Pahad said that a group of observers from Sadc who have begun taking up their posts ahead of the run-off would not merely sit back and watch proceedings but would also actively intervene if deemed necessary.

"They have to ensure the elections take place within the constitution, within the Sadc guidelines and to ensure the people have the atmosphere to vote freely and democratically and that the will of the people is manifested," said Pahad.

AFP