On Monday, the parliament voted for a new constitution which changes the presidential system to a parliamentary one.

But with less than a month before legislative elections, the opposition fears the change will clear the way for the long-serving President, Faure Gnassingbe, to remain in power indefinitely.

Around 30 police officers armed with truncheons broke up the gathering called by opposition parties and civil society groups on Wednesday.

Police said the event in the capital, Lome, was not authorised.

Nathaniel Olympio, the event organiser, termed the new constitution a "coup" that seeks to deprive the Togolese people of the right to choose their president, AFP news agency reported.

"I call on the Togolese people to stand up and stop this disastrous plan," Mr Olympio said.

It is not clear when the changes, proposed by lawmakers mostly from the ruling Union for the Republic (UNIR), will come into force.