BEIRUT -- Syrian troops and rebels clashed again Thursday in the capital Damascus, a day after what activists described as the heaviest fighting in months in President Bashar Assad's seat of power.

The clashes were inching closer to the heart of the city, but still were focused in outlying neighbourhoods such as Qaboun, Jobar and Zamalka in the northeast and the Palestinian refugee camp of Yarmouk in the south, according to the activist groups Syrian Observatory for Human Rights and the Local Coordination Authorities.

The Observatory, based in Britain, said five people, three of them women, were killed in Yarmouk overnight.

On Wednesday, Damascus witnessed the worst fighting since July, when rebels stormed several neighbourhoods in the city and seized control of them for days until they were crushed in a government counteroffensive.

Damascus residents said Thursday was quieter, but they were still hearing sporadic explosions.

State-run television said rebels fired two mortar rounds at a bus station in the Qaboun neighbourhood of Damascus, killing six people including three children and a woman. The TV, quoting an unnamed Interior Ministry official, said others were wounded in the attack.

The Observatory reported clashes and shelling between troops and rebels near Qaboun, saying several shells hit the neighbourhood. It said the fighting occurred near the highway that links Damascus with the central city of Homs, Syria's third-largest.

In other areas, the Observatory reported heavy clashes between troops and rebels near the northern town of al-Safira, where there have been heavy clashes over the past weeks.

Al-Safira, south of the northern city of Aleppo, is home to military production facilities. The rebels have failed to advance in the area after weeks of intense clashes.

The LCC and Observatory reported violence elsewhere in Syrian including the suburbs of the capital, the eastern region of Deir el-Zour and the southern region of Daraa, where the uprising against Assad began 22 months ago.

Syria's opposition chief, who recently offered a dialogue with the government, demanded that the regime release all female political prisoners or he would scrap his offer.

Mouaz al-Khatib of the Syrian National Alliance said in an interview with the BBC Arabic service aired late Wednesday that the women must be released by Sunday.

Al-Khatib said the release of the women should be the beginning of the release of all political prisoners. He claimed there are 160,000 people, but it is not clear how many of them are women.

Al-Khatib made the offer as the crisis reached a stalemate, with neither side making significant battlefield gains likely to bring about a military victory any time soon.

The fighting, which began in March 2011, has left more than 60,000 dead, according to the U.N.

"The regime has until Sunday to begin releasing detainees, especially women. This should be the introduction of prisoners' release," al-Khatib said. "I warn anyone not to harm any of our women."

"If the women are not released by Sunday I consider that the regime wants to break the initiative," he said.

Al-Khatib's offer, which came last week, sparked criticism from opposition activists who say the regime has killed too many people to play a role in the conflict's solution.

He explained his position further on Monday, preconditioning the talks on Assad's departure and saying they could spare Syrians more suffering.

Al-Khatib's offer followed meetings he had held separately with Russian, U.S. and Iranian officials on the sidelines of a security conference in Munich over the weekend. Russia and Iran are Syria's two closest allies.

The government has ignored al-Khatib's offer for talks.

Prominent Syrian legislator Fayez Sayegh said this week that any dialogue must begin without preconditions. He also called Khatib's number of opposition supporters in custody "exaggerated," although he did not give an alternate number.

Human rights organizations say tens of thousands of opposition members, protesters and their families are being held by state security services.

Washington hailed al-Khatib's willingness for dialogue, but said the offer should not include immunity for those responsible for killing civilians.