(CNN) -- A wave of explosions targeting Syrian government forces killed dozens of people at a popular Aleppo square Wednesday in an attack for which a Syria-based extremist group has claimed responsibility.
Al-Nusra Front said the strikes were carried out by suicide bombers driving cars packed with explosives, followed by raiders disguised in Syrian military uniforms, according to a statement posted on a website that publishes claims from extreme Islamist groups.
''The second explosion happened at 8:17 a.m. outside the Governorate Building where a suicide bomber blew up a car bomb loaded with 500 kg of explosive material," the Interior Ministry said in a statement.
Two mortar shells also fell near the Municipal Palace, it said.
At least 40 people were killed and about 90 were wounded when three car bombs exploded in Saadallah Al-Jabiri Square, according to the Syrian Observatory for Human Rights.
Though Syrian state-run media put the death toll at 34, with 122 injured.
State television, meanwhile, aired footage of the carnage, which included the bloody and mangled bodies of men in military uniforms.
A fourth car bomb exploded near Aleppo's chamber of commerce, the government and opposition said. The number of casualties from that incident was not immediately known.
The blasts highlight the escalating crisis in Aleppo, Syria's most populous city, which has morphed into a major battleground between government and rebel forces.
Aleppo is also a major financial lifeline for President Bashar al-Assad's government; a rebel takeover of the city would deal a significant blow to four decades of Assad family rule.
Opposition groups later reported that "a number of regime forces" had been killed following the shelling of a Syrian military center near the town of Tal Abyad.
The deaths were not part of the Wednesday toll distributed by the opposition Local Coordination Committees of Syria. It said at least 200 people died across Syria on Wednesday, including 67 in Damascus and its suburbs and 29 in Idlib province.
More than 28,000 people have been killed across Syria since March 2011, the LCC says. CNN is unable to independently confirm casualty reports, as the Syrian government has severely limited access by international journalists.
In other developments:
Shelling from Syria strikes house in Turkey
At least five people were killed and 10 injured when a shell landed on a house in the Turkish town of Akcakale, near the Syrian border, the town's mayor said Wednesday.
The artillery shell was fired from the Syrian district of Tel Abayad, according to Turkey's semiofficial Anadolu news agency. However, it is not yet clear what military force or group launched it.
Mayor Abdulhakim Ayhan said those killed were three children, their mother and a female neighbor. Two police officers were among those hurt, he said.
In return, Turkey fired on Syrian government targets.
"Our armed forces on the border responded immediately to this atrocious attack within the rules of engagement, and points in Syria determined by radar were hit with artillery fire," a statement from Prime Minister Recep Tayyip Erdogan's office said. "Turkey, within the confines of the rules of engagement and international law, will never leave these types of provocations aimed at our national security unanswered."
UK steps up aid for Syrian refugees in Turkey
The United Kingdom will provide an additional 1 million pounds ($1.6 million) to help Syrian refugees through the Turkish winter, Deputy Prime Minister Nick Clegg said Wednesday.
"Refugees from Syria face what is likely to be a bitterly cold winter. The supplies this extra funding will deliver will go some way to helping them through this difficult time," Clegg said in a written statement.
The United Kingdom has given 38.5 million pounds ($62 million) in humanitarian aid during the Syrian crisis. The added funding is expected to help about 10,000 refugees with supplies such as blankets, clothing and heaters
Turkey has taken in more than 93,000 Syrian refugees, more than any other country in the region.
CNN's Holly Yan and Ivan Watson contributed to this report.