YEREVAN (AFP) - At least five Armenian civil society activists have been attacked by unidentified assailants while taking part in recent protests in the capital Yerevan, Human Rights Watch said on Thursday.

"A spate of violent attacks against peaceful protesters appears to be a concerted effort to intimidate activists and should be effectively investigated," the New York-based rights group said in a statement.

Two prominent civil society activists were hospitalised last week after taking part in a protest in Yerevan against Armenian President Serzh Sarkisian's decision to join a Russian-led customs union, the rights group said.

Three youth activists were also attacked in two separate incidents on August 25 and September 4 after participating in demonstrations at a municipal building in Yerevan, the statement said.

In a report released last month, Amnesty International said that activists and journalists in the ex-Soviet state face harassment and intimidation for questioning mainstream views in the Caucasus nation.