Activists say the Syrian military has bombarded opposition-held districts of Homs to try to stop rebels from re-capturing their former stronghold in the central city.
The activists said Syrian troops fired rockets at the neighborhood of Baba Amr on Tuesday, using the campus of Baath University as a launching site. They said government forces also shelled the rebel district of Khaldiyeh in Homs.
Syrian rebels infiltrated Baba Amr on Sunday in a bid to re-take the district they lost one year ago after a month-long government offensive that killed hundreds of people.
The Britain-based Syrian Observatory for Human Rights said government and rebel forces also fought around the international airport in Aleppo and nearby military bases on Tuesday.
Rebels who control parts of the northern city have been trying to seize the airport and bases for weeks, but they have faced tough resistance from more heavily-armed troops loyal to President Bashar al-Assad.
Meanwhile, the U.N. children's agency said Tuesday a generation of Syrian children is at risk of being scarred for life by the civil war, which marks its second anniversary this month.
Speaking in Geneva, UNICEF spokesman Patrick McCormick said Syrian children who have seen or experienced only fighting "may end up perpetuating that cycle of violence. "
UNICEF said many children are suffering the trauma of seeing family members and friends killed while being terrified of the sounds of fighting. It said some children also are being deprived of an education because one in five schools has been destroyed, damaged or converted to shelters.
In another development, Israeli President Shimon Peres called on the Arab League to intervene in Syria to "stop the massacre," as he put it. In a speech to the European Parliament in Strasbourg on Tuesday, Peres urged the Arab regional bloc to set up a Syrian provisional government and deploy an Arab force wearing the blue helmets of the United Nations.
The Arab League suspended Syria's membership in 2011, in retaliation for Assad's violent crackdown on government opponents.