The Maldivian Democratic Party (MDP) said Yameen was yet to release any in line with Thursday's shock decision of the apex court to quash the dissidents' convictions.
"Although Yameen has said he will abide by the ruling, he is yet to comply with the order delivered more than 36 hours ago," Colombo-based MDP spokesman Hamid Abdul Ghafoor said on Saturday morning.
The court on Thursday night said that cases against the nine dissidents, including former president Mohamed Nasheed, were politically motivated and asked the government to release them immediately.
It also ordered the reinstatement of 12 legislators who were expelled for defecting, and effectively gave the opposition a majority in the 85-member assembly.
In a statement issued overnight, the joint opposition, which includes Nasheed's MDP, said it feared the regime would ignore the release order and that it would trigger further unrest in the nation of 340,000 Sunni Muslims.
"We are deeply fearful that the government's refusal to implement the Supreme Court order could escalate to unrest and incite violence across the country," the joint opposition said.
Nasheed, the country's first democratically elected president, has urged the government to respect the top court's decision.
The United Nations, Australia, Britain, Canada, India and the United States welcomed the court's decision as a move towards restoring democracy in the politically troubled Indian Ocean nation.
Earlier, Nasheed had said the ruling cleared the way for him to return to the Maldives and contest elections due later this year.
"I can contest and will contest," he told AFP in the Sri Lankan capital Colombo.
For its part, the Maldivian government announced Friday that it had concerns about releasing those who had been convicted for "terrorism, corruption, embezzlement, and treason".
Yameen's office said Attorney General Mohamed Anil had raised the administration's concerns with the chief justice.
Nasheed was barred from contesting any election in the Maldives after a controversial 2015 terrorism conviction internationally criticised as politically motivated.
The Maldives' popular image as an upmarket holiday paradise has been severely damaged by a major crackdown on dissent under Yameen, who has overseen the jailing of almost all his political opponents.
The opposition said there were sporadic clashes Friday night between anti-government activists and the police in the Maldives.
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