Syria protests: Thousands of students rally in Aleppo
Security forces have broken up a demonstration by thousands of students in Aleppo, Syria's second largest city, witnesses and activists say.
The dormitory protest is thought to be the city's biggest so far.
The students demanded an end to the military siege of other cities in Syria including Homs, Deraa and Banias, the main flashpoints of dissent against President Bashar al-Assad's government.
Eighteen people were reported killed on Wednesday amid an ongoing crackdown.
Tanks shelled Homs, the country's third city, and clashes were reported in towns and villages around Deraa, where the protests began in March.
Thousands of people have reportedly been arrested and hundreds killed in the government crackdown.
The Syrian government insists it is pursuing "armed terrorist gangs".
On Wednesday, UN Secretary General Ban Ki-moon called on President Assad to "heed calls for reform and freedom and to desist from excessive force and mass arrest of peaceful demonstrators".
So far untouched
There have been several student demonstrations at Aleppo in past weeks, but they have usually only involved a few hundred people and been swiftly dispersed.
This seems to have been the biggest so far, with several thousand students gathering on the campus on the western side of the city, and chanting slogans in solidarity with Deraa.
As has happened in the past, fellow students loyal to the Assad regime and security agents with batons moved in and dispersed the crowds.
One report said police closed the main road leading from the centre of the city to the campus, in an attempt to keep the crowd from spilling over into the city centre.
Aleppo itself has been largely untouched by the unrest so far.
Analysts say that unless Aleppo, and the Syrian capital Damascus, are fully caught up in the revolt, the protesters' chances of toppling the regime are slim.
The BBC's Jim Muir in Beirut, Lebanon, says the authorities know that and have done everything possible to ensure the flames of protest do not take hold in the two big cities.
However, Homs, the third-biggest city in Syria, is still in the grip of a harsh crackdown by troops and tanks.
One resident there told the BBC that the Bab Amr district had been under siege since Saturday, with no water, electricity or access to medical care.
Shelling began early on Wednesday, and hundreds of troops were reported to have moved in.
Activists told the BBC that about 500 people had been arrested in Homs since Wednesday, including more than 100 on Tuesday night.
It has not been possible to verify the accounts because foreign journalists have not been allowed to enter Syria.
The state news agency, Sana, reported that troops and security agents had "arrested dozens of wanted men and seized large quantities of weapons and ammunition in Bab Amr", as well as in Deraa.
It cited sources as saying that one soldier was killed and four were injured in Bab Amr, while one was killed and another injured in rural Deraa. A number of "terrorists" were killed and injured, it added.
Deraa, where the unrest began in mid-March, has been cut off by troops for more than two weeks, with dozens killed and hundreds arrested.
The government says the situation there is now normal, but it has refused to allow UN humanitarian teams in.
The Syrian Observatory for Human Rights says 647 civilians have been killed since pro-democracy protests began on 18 March. Another rights group, Sawasiah, says more than 800 civilians have died.
Officials dispute the civilian toll and say about 100 soldiers have died.
A mobile phone snapshot, reportedly taken in Qamishli on 29 April, shows protesters carrying banners written in Arabic and Kurdish demanding democracy.
Razan, who is a resident of Damascus, tells the BBC about violence and protests around Syria.
This unverified video seems to show a peaceful protest in Talbisah. Moments into the footage, tanks fire on unarmed civilians. Wyre Davis reports.
Residents of Deraa walk past a burnt-out building. It follows shelling by troops in what human rights groups say was an intensified crackdown on protests in recent weeks.
Syrian army vehicles were photographed near Homs and broadcast on the Syrian opposition internet channel Sham SNN on 11 May.