Tanzania denied claims it was holding three people suspected to be Kenyan National Intelligence Service (NIS) officers.
The officials were said to have arrived in Zanzibar to trace the movements National Super Alliance (NASA) leader Raila Odinga who jetted back into the country on Wednesday night.
Mr Odinga spent a four-day break off the coast of Tanzania mainland.
Tanzania Inspector-General of Police Simon Sirro said his office was not aware of the arrest of any NIS officers from Nairobi.
“I’m not aware of that and what is being speculated about is not true,” he said.
The denial came a day after the government of Zanzibar said it has no information about Mr Odinga’s arrival and holiday.
“We haven’t received any information about his presence. However, we are following up the rumours of his presence,” said Mjini Magharibi Regional Police Commander Hassan Nasir Ali on Wednesday.
While details of what Mr Odinga was doing in Zanzibar remain scanty, photos posted in social media show he was on holiday.
Mr Odinga had on Friday last week arrived to a chaotic welcome at the Jomo Kenyatta International Airport following a 10-day trip in the US.
After the chaos, which involved running battles with the police, teargas, live bullets, burnt cars and left five dead, Mr Odinga flew to Zanzibar due what his long-time adviser Salim Lone said was the unrest in Kenya.