Guinea's President Alpha Conde has set March 22 for the constitutional referendum on his proposed reforms that opponents worry will allow him to bypass term limits and stay in power.

The vote, originally set for March 1 but delayed over local and international concerns about its fairness, will take place at the same time as legislative elections, a presidential decree said on Friday.

The campaign will run until March 20 despite some restrictions put in place on rallies since the first case of coronavirus was confirmed in the country.

The West African country has seen huge opposition rallies over the proposal to change the constitution, which many fear will allow Conde, 82, to seek a third term in office this year.

Since the protests began in October at least 31 protesters and one gendarme have been killed, according to an AFP tally.

International powers have voiced concern over the referendum, and a US official on Friday renewed a call for an investigation into the deaths since October.

"The United States remains concerned about the Government of Guinea's plans to hold legislative elections and a constitutional referendum," a State Department official said.

"We continue to urge all parties to engage in nonviolent civil dialogue," he said.

The former French colony's constitution now mandates two five-year presidential terms. Under the new constitution, there would be two six-year terms.

But critics say the new constitution would also reset the term counter to zero, allowing Conde to run again when his second term ends this year, a possibility the government has not denied.