A UN expert on Wednesday condemned Greece's migration policy for focusing on security issues and creating "an atmosphere of fear" among migrants and their advocates.
That policy was having a "suffocating effect" on civil society, said Mary Lawlor, the UN Special Rapporteur for rights defenders.
"The government's current approach to the issue is defined by its framing of migration as a matter of security and prevention," said Lawlor following a 10-day research trip to Greece.
"What this has fostered for refugees, asylum-seekers, migrants and the human rights defenders acting in solidarity with them, is an atmosphere of fear -- particularly a fear of criminalisation," she added.
Athens has promoted its success in preventing tens of thousands of migrants entering the country.
But Lawlor's visit comes after repeated accusations by rights campaigners that the Greek coastguard has been illegally forcing migrants to return to Turkey.
Athens has denied the allegations, but both the European Union and the UN refugee agency UNHCR called for an investigation.
In March, the country's national transparency authority said a four-month investigation had found no evidence of such practices.
But in her statement Wednesday, Lawlor said government policy and statements by senior officials had heaped pressure on organisations working to defend migrants' rights.
"At the tip of the spear are prosecutions, where acts of solidarity are reinterpreted as criminal activity, specifically the crime of people smuggling," Lawlor said in a statement.
"The negative impact of such cases is multiplied by smear campaigns perpetuating this false image of defenders."
Since he was elected three years ago, conservative Prime Minister Kyriakos Mitsotakis has increased security on the border with Turkey with the help of the EU border agency Frontex.
Lawlor travelled around Greece from June 13-22 at the invitation of the government, interviewing, migrants, rights activists and other interested parties.
She is due to report back to the UN Human Rights Council in March 2023.