The European Union's foreign affairs chief has called on Azerbaijan to provide a “fair and transparent” appeal process for 13 activists jailed for participating in an unauthorized pro-democracy protest.

In a statement Wednesday, Catherine Ashton said she reiterates the importance the EU attaches to freedom of assembly and freedom of expression. She said the EU is ready to assist Azerbaijan in the implementation of democratic reforms.

On Monday, a court sentenced four opposition activists who participated in the protest to jail terms ranging from 18 months to three years for their alleged roles in an April demonstration in Baku. The protest, inspired by the Arab Spring uprisings in Tunisia and Egypt, was broken up by riot police.

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.

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.