Tanzania's main opposition leader Freeman Mbowe has been released after spending more than seven months in custody on terrorism charges.
His supporters said the case was a politically motivated move to crush dissent in the country.
His release is seen as a sign that the government could be about to allow the opposition to operate more freely, analysts say.
The prosecution did not explain why it had decided to drop the charges.
The BBC's Aboubakar Famau in Tanzania says that hundreds of people cheered outside the court when the decision was announced.
The US ambassador to Tanzania, Donald Wright, welcomed Mbowe's release and tweeted that this was "a welcome opportunity for Tanzania to turn the page and focus on the future".
Mbowe's defence lawyer, Peter Kibatala, welcomed his client's release as a "huge victory" adding that "no stone was left unturned".
Mbowe, 60, is the chairman of Chadema, one of Tanzania's main opposition parties. He had been a staunch opponent of the late President John Magufuli, who was nicknamed the bulldozer and accused of cracking down on dissent.
When President Samia Hassan took power a year ago after Magufuli died, it was hoped that she would break from her predecessor's authoritarian approach, but Mbowe's arrest seemed to dash those hopes.
Mbowe and other senior Chadema figures were arrested in July 2021 in a night raid in Mwanza, ahead of a public rally to demand constitutional reforms.
His arrest came at a time of heightened tension after Chadema had launched a nationwide campaign for a constitutional review, a demand that the president said was not her priority. She on several occasions stressed that her priority was fixing the economy.
However, his release could suggest President Samia is seeking to reconcile with the opposition.
In February, while attending the EU-Africa summit, she met another leading Chadema figure, Tundu Lissu. He has been living in exile since he survived an assassination attempt in 2017 in the capital Dodoma.
He was an MP and Chadema's presidential candidate in 2020, when he returned to the country to campaign. He left again shortly afterwards, complaining of widespread fraud after Magufuli was declared the winner.
Some observers think that Mbowe's release, along with the meeting with Lissu, indicate that Tanzania's ruling party, CCM, is signalling that change is underway.
In recent weeks some banned Swahili newspapers have been allowed to resume, including one owned by Mbowe.
Mbowe's release comes just a week before President Samia marks her first anniversary in office.
