Several members of the coalition of politicians and activists that called the demonstrations were arrested, the BBC reported.
According to the British broadcaster, one protester – a student – was killed in the capital, Conakry. A second youth died in the northern city of Labe.
Conakry, the capital city of the West-African nation, was largely deserted on Monday, with businesses, schools and markets staying closed.
Guinea’s president, Alpha Condé, has been in power since the country’s first democratic elections in 2010, winning a second five-year term four years ago.
Under the constitution, a president can serve two five-year terms. But ahead of next year’s election, government officials and allies of Condé have been dropping hints about amending the constitution or writing a new one to let him stand again.
Conde’s opponents fear a new constitution could be used as a reset button on his presidency, allowing Conde to run again like other African leaders who have amended or changed constitutions in recent years to stay in power.
The government has said it would investigate the deaths during the protests, which opposition leaders and residents said were caused by security forces’ opening fire on demonstrators.