Diplomats in Athens believe some criticism of police tactics is justified
Amnesty International has accused Greek police of serious rights violations and called on the government to set up an inquiry into "systemic problems".
The rights group said the response to December's riots in Athens was the culmination of an "entrenched pattern of serious human rights violations".
The anti-government protests erupted after police shot dead a teenaged boy.
In the following weeks police faced almost daily demonstrations and riots, and have come under armed attack.
The Greek government has not responded to the Amnesty report, but diplomats said the police have shown considerable restraint in the circumstances.
In January, a policeman was shot and seriously wounded in central Athens in an attack claimed by the left-wing militant group, Revolutionary Struggle.
It was one of several such armed attacks.
In a report published on Monday, Amnesty said that since the end of the anti-government demonstrations in January it had received mounting allegations of human rights violations by police.
The group said it had brought a number of cases to the attention of Interior Minister Prokopis Pavlopoulos, in which police officers were said to have arbitrarily arrested, ill-treated and detained peaceful demonstrators and prevented detainees, including minors, from promptly contacting their lawyers.
During one incident on 9 January, several lawyers were reportedly arrested and mistreated after a violent demonstration on Asklipiou Street in Athens, Amnesty said.
Video footage showed police refusing to answer any questions and later dragging an elderly woman along the pavement, it added.
"Time and again police officers in Greece have been accused of using excessive force against demonstrators or denying them their rights when in detention," said Nicola Duckworth, director of Amnesty's Europe and Central Asia programme.
"The police response to the recent unrest is the culmination of an entrenched pattern of serious human rights violations by law enforcement officials."
Ms Duckworth said such incidents "should be used as a catalyst by the government to launch a wide-ranging commission of inquiry that would investigate not only recent events but also systemic issues, including training of police on the use of firearms and of force".
Greek police have protested against the repeated attacks of recent months
"The people of Greece have the right to proper policing in accordance with the government's national and international obligations," she added.
Union officials representing the police say morale in the force is at an all-time low, because of poor pay, insufficient training, and most important of all, the pledge by left-wing militants to kill an officer in retaliation for the shooting of teenager Alexis Grigoropoulos in December.
The BBC's Malcolm Brabant says foreign diplomats based in Athens believe that some criticism of police tactics is justified, but say few other European police forces would be as tolerant as the Greeks when facing such violence.