Thousands of people have taken to the streets in numerous parts of Aleppo, Syria's second city, to protest against the Syrian government's crackdown on dissent, amid growing unrest related to the nationwide uprising.

Syrian security forces killed at least three people on Wednesday after opening fire on demonstrations in the towns of Sheikh Issa, Hreitan and Aleppo city - the capital of the governorate, the Syrian Observatory for Human Rights, a UK-based activist group, reported.

Aleppo, Syria's main trade and financial centre that had also been largely quiet allegedly because it was a stronghold of support for President Bashar al-Assad, has seen a significant rise in anti-government protests in recent months.

At Aleppo University, where massive anti-government protests have persisted since the uprising began in March last year, fresh demonstrations were reportedly crushed by security forces, who arrested a number of students.

Similiar to Aleppo, Latakia - a coastal province that had also seen limited protests during the uprising, is also seeing a serious increase in dissent.

Government forces used tanks and attack helicopters to continue shelling towns in Latakia for a second day, killing at least six people on Wednesday. 

The attacks, which killed a family of three in al-Shirqaq and another three people in al-Heffa, came a day after about 33 people were killed during clashes between soldiers and army defectors in the province.

At least 22 troops, nine defectors, and two civilians were killed in the fighting on Thursday in Latakia, the Syrian Observatory for Human Rights reported.

The Syrian National Council, the country's main political group, called on "UN observers to go to the town of al-Heffa immediately, in order to prevent a new massacre".