A court in Azerbaijan has sentenced four opposition activists to jail terms ranging from 18 months to three years, in the latest convictions resulting from an unauthorized pro-democracy protest.

The men were sentenced Monday for their alleged roles in an April demonstration in Baku inspired by the Arab Spring uprisings in Tunisia and Egypt. The demonstration was broken up by riot police.

Supporters outside the courtroom chanted “Freedom” and sang Azerbaijan's national anthem in protest.

Monday's sentences follow the jailing last week of three opposition party officials for two-and-a-half years on similar offenses. The opposition says they were sentenced without any evidence that could substantiate they were guilty.

The latest convictions bring to 13 the number of opposition activists jailed for participating in protests that sought to replicate the Arab Spring uprisings.

After last week's verdicts, the rights group Amnesty International accused Azerbaijani authorities of “targeting leading activists in an attempt to silence the opposition” and dissuade others from speaking out.

Last month, Europe's main human rights body, the Council of Europe, expressed concern about a lack of progress on the human rights situation in Azerbaijan.

Police in Baku arrested activists and political opponents during protests in March and April. Six opposition activists were convicted of disturbing public order and sentenced in August following questionable trials.

Rights groups have long criticized the oil-rich former Soviet republic for clamping down on dissent.

Azerbaijani officials insist the country fully enjoys freedom of speech and assembly.