Soldiers and police were patrolling Mozambique's capital, Maputo, early on Thursday ahead of a planned protest against election results rejected by the opposition.
Violence has shook the southern African nation since the Frelimo party, which has ruled for nearly 50 years, won an election on October 9.
The city of more than one million people was a ghost town on Thursday morning, with shops, banks, schools, and universities closed.
A group of a dozen demonstrators gathered on one of the main streets before being told by a soldier to go home.
Disputed results
Frelimo's Daniel Chapo won the presidential election with 71 percent of the vote, according to the electoral commission, while the main opposition candidate Venancio Mondlane came in second with 20 percent.
Mondlane, backed by the Podemos party and who said results were false and that he won, called for a mass protest on Thursday.
Using social media, he has rallied supporters out onto the streets since the election in demonstrations that have turned violent in police crackdowns.
In an interview with AFP, the opposition leader, whose whereabouts are unknown, said he would not be present at the march due to concerns over his safety.
At least 18 killed
At least 18 protesters have been killed in post-electoral violence, according to Human Rights Watch.
Local NGO, the Centre for Democracy and Human Rights (CDD), said the death toll was 24.
A police officer was also killed in a protest at the weekend, Defence Minister Cristovao Chume told reporters on Tuesday, warning the army could intervene "to protect the interests of the state."
"There is an intention to change the democratically established power," he said, amid fears that outgoing President Filipe Nyusi could declare a state of emergency.
Nyusi is expected to step down early next year at the end of his two-term limit.
Internet restrictions
The authorities have restricted access to the internet across the country in what seemed like an effort to "suppress peaceful protests and public criticism of the government," according to Human Rights Watch (HRW).
"The shutdown inhibits people's ability to receive and use life-saving information, to assemble peacefully, and to express their political opinions in a time of crisis," said Allan Ngari, Africa advocacy director at HRW.
The United Nations High Commissioner for Human Rights, Volker Türk, said on Wednesday that he was "deeply alarmed by reports of violence across the country."
"The police must refrain from using unnecessary or disproportionate force and ensure that they manage protests in line with Mozambique's international human rights obligations," he said.
The Southern African Development Community has called for an extraordinary summit between November 16 and 20 to discuss developments in Mozambique.
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