Tanzanian President Samia Suluhu on Monday said foreign activists would not be allowed to “interfere” in the country's affairs after several tried to attend the trial of opposition leader Tundu Lissu, who is facing treason charges.

"We have started to observe a trend in which activists from within our region are attempting to intrude and interfere in our affairs," Hassan said in a televised speech during the launch of the country’s new foreign policy.

“If they have been controlled in their country, let them not come to disrupt us. Let us not give them the chance; they have already destabilised their countries and the only remaining peaceful nation is Tanzania.”

Suluhu urged the country’s security and defence organs “not to allow ill-mannered individuals from other countries to cross the line here."

Her comments came just hours after several Kenyan rights activists were denied entry to Tanzania and deported to Nairobi.

PLP leader and former Justice Minister Martha Karua and former Chief Justice Willy Mutunga were among those detained when they landed at Tanzania's Julius Nyerere International Airport in Dar es Salaam, to observe Lissu’s case hearing on Monday.

Lissu, the leader of Tanzania’s main opposition party Chadema, was charged with treason over an alleged speech calling on Tanzanians to rebel and disrupt the country’s presidential and parliamentary elections due in October.

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In April, his party was disqualified from competing in the upcoming polls after the National Electoral Commission said that the party had failed to sign a code of conduct document.

Chadema accuses Suluhu’s government of returning to the repressive policies of the recent past.

Lissu's case was adjourned to June 2, as the prosecution said investigations were ongoing.