Updated at 10:42 a.m. ET
BEIRUT - Two explosions struck security compounds in Aleppo on Friday, killing 28 people, state media reported, the first significant violence in a major city that has largely stood by Syrian President Bashar Assad in the 11-month-old uprising against his rule.
The blasts come as escalating violence between regime forces and an increasingly militarized opposition has raised fears the conflict is spiraling toward civil war.
A Syrian offensive aimed at crushing rebels in the battered city of Homs continued Friday, with soldiers who have been bombarding the city for the past six days making their first ground move to seize one of the most restive neighborhoods.
State TV blamed "terrorists" for the blasts in Aleppo, Syria's largest city, and said they were proof the government is facing a violent enemy. Anti-Assad activists accused the regime of setting off Friday's blasts to discredit the opposition and avert protests that had been planned in the northern city on Friday.
Capt. Ammar al-Wawi of the Free Syrian Army, a rebel group that wants to bring down the regime by force, denied involvement.
"This explosion is the work of the regime to divert world attention from the crimes it is committing against the people of Homs," he said.
Along with the capital Damascus, Aleppo is Syria's economic center, home to the business community and prosperous merchant classes whose continued backing for Assad has been crucial in bolstering his regime. The city has seen only occasional protests.
Eyewitnesses tell CBS News' George Baghdadi in Damascus that the two blasts went off within moments of each other, echoing across the city.
"The walls and beds have shaken. The kids started to cry. It was really frightening," Mayada, a mother of three told CBS News via telephone.
Three earlier bombings in Damascus in December and January that killed dozens prompted similar exchanges of accusations. Nobody has claimed responsibility for any of the attacks.
Syria has banned foreign journalists from operating independently in the country, but CBS News correspondent Clarissa Ward sneaked into Syria and has been living alongside the rebel fighters as they battle Assad's forces in northern Syria - the clashes are not limited to Homs, by any means.
More reports from Clarissa Ward inside Syria:
Outside one of the compounds hit, the Military Intelligence Directorate, a weeping correspondent on state-run TV showed graphic footage of at least five corpses, collected in sacks and under blankets by the side of the road.
Debris filled the street and residential buildings appeared to have their windows shattered. But the location did not appear to be closed off, and local residents milled around the site with few uniformed police around.
There was no immediate sign of wounded. Earth-moving equipment was seen clearing the rubble.
The TV presenter said the blast went off near a park and claimed children were among the dead, although none were seen in the TV footage.
The second blast went off outside the headquarters of a police force in another part of the city. State television cited the Health Ministry as saying 25 people were killed in the two blasts and 175 were wounded.
Mohammed Abu-Nasr, an Aleppo-based activist, said the blasts came on a day when activists were planning wide protests in the city after the Friday prayers. He said several hundred people showed up for the protests despite the bombings in different parts of the city.
The Britain-based Syrian Observatory for Human Rights and the Local Coordinating Committees activist group said security forces opened fire, killing at least seven people. The figures were impossible to confirm.
So far, Assad's opponents have had little success in galvanizing support in Aleppo, in part because the business leaders have long traded political freedoms for economic privileges.
The city of around 2 million also has a large population of Kurds, who have mostly stayed on the sidelines of the uprising since Assad's regime began giving them citizenship, which they had long been denied.
Assad's crackdown has killed more than 5,400 people since the uprising began in March.
The regime's crackdown on dissent has left it almost completely isolated internationally. But Assad has political backing from Russia and China, which delivered a double veto over the weekend that blocked a U.N. resolution calling on him to leave power.
Russian Deputy Foreign Minister Sergei Ryabkov signaled Friday that Moscow will again use its veto power at the United Nations to block any resolution aimed at ousting Assad.
"If our foreign partners don't understand that, we will have to use strong means again and again to call them back to reality," he was quoted as saying by the ITAR-Tass news agency. Moscow's stance is motivated in part by its strategic and defense ties, including weapons sales, with Syria. Russia also rejects what it sees as a world order dominated by the U.S. Last month, Russia reportedly signed a $550 million deal to sell combat jets to Syria.
The assault on Homs began last Saturday after unconfirmed reports that army defectors and other armed opponents of Assad were setting up their own checkpoints and taking control of some areas.
Hundreds of people are believed to have been killed in the past week in Homs from relentless shelling and gunfire on several rebellious neighborhoods in the city, an operation activists said aimed to soften up the areas before moving in.
"They are punishing the residents," said the Observatory's chief Rami Abdul-Rahman, who added that food supplies were dwindling in the area.
Troops shelled parts of the city with tanks and heavy machine guns through the night until daylight Friday, said Majd Amer, an activist in Khaldiyeh, one of the targeted districts. He said troops nearby appeared to be preparing to move into Khaldiyeh as well.
Mohammed Saleh, a Syria-based activist, said the regime appears to be trying to take over rebel-held areas in Homs and the northwestern restive province of Idlib before Feb. 17, when Assad's ruling Baath party is scheduled to hold its first general conference since 2005.
The conference is expected to move on reforms that Assad has promised in a bid to calm the uprising. During the conference, Baath party leaders are expected to call for national dialogue and announce they will open the way for other political parties to play a bigger role in Syria's politics.
The opposition has rejected such promises as insincere and said it will not accept anything less than Assad's departure.