At least 15 people were injured when opposition supporters stoned the headquarters of the Guinean ruling party in Conakry, the Rally for Guinean People (RPG) said Sunday.

Secretary general Saloum Cisse said "unidentified individuals attacked the national headquarters of our party on Saturday, throwing stones and hitting people with batons, breaking the windows of a dozen cars parked outside."

He said the attack had taken place after a convoy of opposition leaders passed in front of the building. The incident took place on the sidelines of an opposition rally which police broke up using tear gas.

Traore Zalikatou Diallo, secretary general of the Party of Hope for National Development (PEDN) of former prime minister Lansana Kouyate, said the party's convoy had been attacked by stone-throwing supporters of the ruling party.

"Afterwards our supporters retaliated ... he who sows the wind reaps the whirlwind."

Members of the RPG on Sunday morning attacked the PEDN headquarters in Kouroussa 500 kilometres (310 miles) east of the capital.

Saturday's opposition rally in Conakry was held to demand transparent legislative polls in July.

The delayed polls should have been held six months after Conde took office in November 2010 in Guinea's first democratic presidential election, held to fanfare after a period of turmoil under a military junta which took over in 2008.

The opposition has accused the regime of planning to hold sham polls with no safeguards against fraud, and wants the electoral register to be audited before they take place.

The last legislative elections were in June 2002 during Conte's 24-year rule.

A transitional council has served as a parliament since 2010 to help ease out military rule.