The opposition held the first of three planned demonstrations this week on Tuesday, calling for constitutional reform and the resignation of President Faure Gnassingbe.
But it said its supporters were prevented from taking to the streets in the northern cities of Sokode and Bafilo, despite government permission.
Heavily armed soldiers with their heads and faces covered positioned themselves at the starting points of the protests, breaking up crowds with sticks and tear gas.
In Sokode -- the stronghold of opposition leader Tikpi Atchadam -- the opposition said 16 people were injured by gunshots and beatings and three in Bafilo, where one disabled person was beaten up.
Amnesty International said it counted "at least 10 injured" in hospital in Sokode on Tuesday afternoon, including one with gunshot wounds in intensive care.
"There are others in houses," making an exact number difficult to ascertain, the organization’s country director Aime Adi told AFP by telephone.
"The coalition condemns in the strongest terms this savage repression and the doublespeak of the regime," the opposition said in a statement.
On Monday, the government had indicated it was open to talks with the opposition and announced the release of 42 people arrested during previous demonstrations.
Since the first protests began in late August, at least 16 people have died and more than 200 others have been injured as hundreds of thousands took to the streets across the country.
Demonstrators were again out in force on Wednesday and are expected again on Thursday.
In a joint statement, the European Union, United Nations and the French, US and German embassies said they welcomed the government's measures to calm the situation.
It appealed for protests to take place peacefully.
The opposition wants Gnassingbe to step down and the introduction of a two-term limit for presidents, applied retroactively to prevent Gnassingbe standing for re-election.
Gnassingbe has been in power since 2005 and won three elections. His father General Gnassingbe Eyadema was president before him and ruled for 38 years.