The Guinean government warned it will respond vigorously to any violence at an opposition rally on Monday, the latest protest over fears that President Alpha Conde is changing the constitution to extend his mandate.
The West African country has been wracked by mass demonstrations since mid-October over constitutional reform.
At least 20 civilians and one gendarme have been killed in the protests, which have drawn hundreds of thousands of people. Scores have been arrested.
For Monday the National Front for the Defence of the Constitution (FNDC), an alliance of opposition groups, has called for a "huge" and "open-ended" protest, heightening fears of fresh violence.
While the FNDC also specified a peaceful demonstration, the government issued a statement Sunday accusing the opposition leaders of seeking "to plunge Guinea into disorder".
"State powers will be exercised in all their rigour against those who seek to upset public order and to deny other Guineans the free exercise of their fundamental rights," the statement said.
Conde, 81, published a draft constitution last month, arguing that the colonial-era laws need to be changed.
But adversaries are convinced he plans to use the reform to stay in office beyond the two presidential terms currently stipulated in the former French colony's constitution.
The president has neither confirmed nor denied that claim.
Guinea, a mineral-rich but poor country of some 13 million, is facing a busy political year.
Legislative elections are due in February and a presidential election is scheduled sometime this year, as well as a possible referendum on the constitution.
However, opposition political parties are boycotting the legislative elections and have vowed to prevent them.
Conde, who was jailed under Guinea's previous authoritarian regimes, became the first democratically elected president in 2010.
Despite initial hopes of a new political dawn, critics say Conde's rule has become increasingly authoritarian.
The protests against his constitutional plans began in October, without any official authorisation.
More recently they have been authorised under strict conditions.
Human rights defenders have accused the government of using excessive force and arbitrary arrests.
Tensions were further heightened at the end of the past week by a teachers' strike over salaries.
An 18-year-old woman and a 21-year-old man were shot dead during protests Thursday.
Eleven union members were arrested on Saturday, according to a union official.