Syrian rebels battled government troops near a landmark 12th century mosque in the northern city of Aleppo on Tuesday, while fierce clashes raged around a police academy west of the city, activists said.
The fighting near the Umayyad Mosque in the walled Old City threatened to further damage the historic structure, part of which was burned during clashes last year.
Since July 2012, government forces and rebels seeking to topple President Bashar Assad have been battling over Aleppo, the country's largest city and a major prize in the civil war. While rebels have gradually expanded the amount of turf under their control, seven months of street fighting, airstrikes and shelling have left much of the city, considered one of Syria's most beautiful, in ruins.
The Britain-based Syrian Observatory for Human Rights reported intense clashes with heavy gunfire and explosions near the mosque. Syria's state news agency said "terrorists" had detonated explosives near the building's south wall, causing "material damages."
Assad's regime refers to the opposition as "terrorists."
The mosque, also known as the Great Mosque of Aleppo, sits near a medieval covered market in the Old City, which is a UNESCO World Heritage site. The mosque was heavily damaged in October, 2012, just weeks after a fire gutted the market.
Syria's nearly 2-year-old civil war has left its mark on other gems of the country's rich archaeological and cultural heritage.
At least five of Syria's six World Heritage sites have been damaged in the fighting, according to UNESCO, the U.N.'s cultural agency. Looters have broken into one of the world's best-preserved Crusader castles, Crac des Chevaliers, and ruins in the ancient city of Palmyra have been damaged.
Both rebels and regime forces have turned some of Syria's significant historic sites into bases, including citadels and Turkish bath houses, while thieves have stolen artifacts from archaeological excavations and, to a lesser extent, museums.
To the west of Aleppo, activists reported fresh fighting Tuesday near the police academy that has become a key government military installation.
The Observatory said the two sides were shelling each other's positions while the government launched airstrikes in the area.
Video posted online in recent days shows rebel groups firing homemade rockets and mortars at the academy and blasting it with captured tanks. The videos appeared genuine and corresponded with other Associated Press reporting.
The Observatory said the dead in the last two days of fighting in the area included 26 rebel fighters, 40 soldiers and five pro-government militiamen.
The police academy, which activists say the government has turned into a military base, has recently emerged as a new front in the battle for Aleppo. Losing the facility would hinder the regime's ability to shell opposition areas and support its troops inside the city.
An Aleppo activist who goes by the name Abu al-Hassan said via Skype that rebels coming from Idlib province to the west are now trying to clear the army from residential areas near the academy before they attack it.
"Yesterday and today they have been trying to go forward but there are lots of shelling and airstrikes," he said.
The fighting has largely destroyed Aleppo and caused humanitarian conditions for the city's remaining civilians to plummet.
On Tuesday, Human Rights Watch said more than 141 people, including 71 children, had been killed in at least four missile strikes by the Syrian government in and near the city of Aleppo last week. The New York-based group said the strikes hit residential areas and called them an "escalation of unlawful attacks against Syria's civilian population."
A Human Rights Watch researcher who visited the sites said up to 20 buildings were destroyed in each area hit by a missile. There were no signs of any military targets in the residential districts, located in rebel-held parts of Aleppo and its northern countryside, said Ole Solvang, the researcher.
"The extent of the damage from a single strike, the lack of (military) aircraft in the area at the time, and reports of ballistic missiles being launched from a military base near Damascus overwhelmingly suggest that government forces struck these areas with ballistic missiles," HRW said in its report.
It added that the Aleppo neighborhoods hit were Jabal Badro, Tariq al-Bab and Ard al-Hamra. The fourth strike documented by the group was in Tel Rifat, north of the city.
UNICEF said in a statement that it is "appalled" by the deaths of children, and called on all parties in the conflict to "ensure that civilians — and children especially — are protected, at all times."
U.N. political chief Jeffrey Feltman condemned the bombings in Aleppo and Damascus and repeated a call "to immediately end the supply of arms to both sides in this brutal conflict." He pledged that "perpetrators of serious crimes will be held accountable."
Syria has never acknowledged the strikes, and portrays the conflict as a foreign conspiracy carried out by "terrorists" to weaken the country.
The missile attacks have outraged the leaders of Syria's exiled opposition who have accused their Western backers of indifference to the suffering of civilians caught up in the conflict.
Also Tuesday, the Observatory said the death toll in a car bomb attack in Damascus had risen to eight. All were regime security officers, it said.
The blast late Monday struck a security checkpoint in the neighborhood of Qaboun, less than a kilometer (mile) from Abbasid Square, northeast of downtown. It was followed by several other smaller blasts thought to be mortar shells landing in various districts of the capital.
The explosions and subsequent gunfire caused panic among residents who hid in their apartments.
Syria's state news agency said the blast was caused by a suicide car bomber and caused an unspecified number of casualties.
The U.N. says some 70,000 have been killed since Syria's conflict began in March 2011.
Associated Press writer Ryan Lucas in Beirut and Edith M. Lederer at the U.N. contributed.