Tanzanian authorities arrested a senior opposition official as he was departing for a political conference in Belgium, his party said on Tuesday, as fears grow of an escalating crackdown ahead of an October election.

While President Samia Suluhu Hassan, who plans to seek reelection, says the government is committed to respecting human rights, a recent string of high-profile arrests has thrust her record into the spotlight.

Amani Golugwa, a senior member of Tanzania's main opposition CHADEMA party, was arrested at Julius Nyerere International Airport in the capital Dar es Salaam on Monday, his party wrote on X.

Tanzanian police confirmed his arrest in a post on their Instagram account, writing that Golugwa "has a trend of leaving and returning to the country without following legal procedures."

"Dar es Salaam police special zone is continuing with the investigation on the matter in collaboration with other security organs," the post added.

A government spokesperson did not immediately respond to a request for comment.

Golugwa had been due to represent his party in Brussels at a forum organised by the International Democracy Union, a grouping of centre-right parties that CHADEMA belongs to and which also counts the British Conservatives and U.S. Republicans as members.

"The IDU strongly condemns the unlawful arrest and assault of CHADEMA's (Golugwa)," the organisation posted on X. "Silencing opposition voices violates the core of democracy. We call for his immediate release."

Police arrested Tundu Lissu, CHADEMA's leader and Tanzania's main opposition figure, last month.

Lissu, who was shot 16 times in a 2017 attack and came second in the last presidential poll, was subsequently charged with treason over what prosecutors said was a speech calling upon the public to rebel and disrupt the elections.

He had held several rallies in early April under the slogan "No Reforms, No Election", where CHADEMA demanded significant changes to an electoral process they say favours the ruling party.

Days after Lissu's arrest, the election commission disqualified CHADEMA from participating in the polls over its refusal to sign a code of conduct.