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At least 34 people have been killed and dozens wounded in a series of bomb explosions in the centre of Syria's second city, Aleppo.
The attacks levelled buildings in the city's main square.
A military officers' club and a hotel being used by the military bore the brunt of the blasts, some of which were carried out by suicide car bombers.
Aleppo has become a key battleground between rebels and forces loyal to President Bashar Assad.
The extraordinary series of explosions that devastated Saadallah al-Jabari Square in central Aleppo came at a moment when regime forces were supposedly preparing for a major operation to drive rebels out of the city once and for all, after more than two months of inconclusive struggle.
Such spectacular attacks, believed to be suicide operations by Islamist militants, normally have little effect on the overall stategic situation but have a propaganda and psychological impact, and may damage morale in government-held areas.
These particular bombings apparently targeted the military officers' club and a hotel taken over by government forces. With many military personnel among the casualties, it's possible that the planning and direction of the regime campaign to oust the rebels may have been affected.
When jihadi Islamists and suicide bombings first appeared on the scene last December, they were condemned by the opposition and suspected of being manipulated by the regime.
But now the situation has become so militarised, and jihadis so embedded in the struggle in places like Aleppo, that such condemnation is unlikely, despite the fact that many civilians were also among the casualties.
Rebels have not been able to take over the city, but government forces - despite massive bombardments by artillery, tanks and aircraft - failed to dislodge opposition fighters.
There are reports that regime forces are preparing for a major offensive.
The Syrian Observatory for Human Rights, a UK-based activist group, quoted medical sources as saying that most of the dead in Wednesday morning's bombings in Saadallah al-Jabari Square were regime troops.
Syrian government officials and other witnesses, however, said many civilians had been killed.
Footage from the scene showed bodies being carried away, with blankets being used as stretchers.
"It was like a series of earthquakes," a shaken resident was quoted as saying by the Associated Press. "It was terrifying, terrifying."
He said the officers' club and the hotel were almost completely destroyed.
State television said that after the explosions, two or three "terrorists" appeared wearing military uniforms and explosive vests, but were shot dead before they could carry out any attacks.
There was no immediate claim of responsibility for the attacks. Syria's state-run Sana news agency said the bombings were carried out by "terrorists".
The speaker of the Syrian parliament, Jihad al-Laham, said foreign powers supporting opposition rebel groups were responsible.
Bombings - many of them targeting security facilities - have become increasingly common in the Syrian conflict, which began in March last year and has seen protests for political reform develop into an armed insurgency that has reportedly left tens of thousands dead.
On 18 July, rebels bombed a complex in the capital Damascus, killing four senior security officials, including President Assad's brother-in-law and the defence minister.
Attempts to address the conflict at the United Nations have been blocked by a standoff in the Security Council between Russia and China, traditional Assad supporters, and Western powers seeking a tougher stance against the Syrian regime.
Wednesday also saw shells from Syria kill five people - including three children - in the Turkish town of Akcakale, in southern Sanliurfa province.
Turkish officials said at least nine others were seriously wounded, including three police officers.