Lusaka: Embattled Zambian ex-president Rupiah Banda was on Friday blocked from leaving the country but said he was unfazed by his "persecution."

Zambian immigration authorities prevented the 76-year-old from leaving the country for the third time in nearly two months, sparking widespread criticism from activists.

"No, no I am not heart broken by these persecutions and I have to be strong," Banda told AFP.

Banda, who is fighting corruption charges, was stopped from boarding a flight to South Africa despite a High Court order releasing his passport.

A raft of criminal charges were brought against him by his successor`s administration led by Michael Sata which took office in September 2011. He has maintained that the charges are politically motivated.

"At least I am happy that when I was president I did not do this to anybody," he said.

"If I had done something like that my conscience would not be clear."

Banda accused the country`s chief prosecutor Mutembo Nchito of harbouring great hatred against him.

The former head of state was set to fly to South Africa on a morning flight today for a conference.

His planned trip was marred by problems after a magistrate`s court refused to return his passport, which he had to surrender after his re-arrest in April on corruption charges. He later approached the High Court which released the travel document.

"We did all the airport formalities but surprisingly an immigration officer came and said he had instructions from above not to allow president Banda to travel," his press aide Kennedy Limwanya told AFP.

"We showed him a court order but he still said he could not allow us."

The government today said it had slapped Banda with a formal travel ban.

"The investigations team has imposed travel embargoes against the former president for fear that he might interfere with the witnesses," said Home Affairs Minister Edgar Lungu.

Rights groups today strongly condemned the government`s refusal to allow Banda`s travels.

"Banda is a former head of state and he followed the normal channels to get his passport," said Bishop John Mambo of the Bible Gospel Church in Africa.

The consortium of 11 organisations said Banda was not a flight risk.

"He is not under house arrest. Let him be allowed to travel," said Mambo, a vocal critic of the Sata administration.

AFP