Police in Togo have broken up an opposition news conference that was called to address a controversial constitutional reform.

On Monday, the parliament voted for a new constitution that changed 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 authorized.

Nathaniel Olympio, the event organizer, 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.