Syrian rights activists say a battle between government and rebel forces in the southern province of Daraa has killed at least 50 people, more than half of them civilians.
The Britain-based Syrian Observatory for Human Rights said the fighting happened Wednesday as troops loyal to Syrian President Bashar al-Assad launched an assault to oust rebels from the town of Sanamein.
Rebel fighters have made steady territorial gains in southern Syria in recent weeks, in a bid to control access routes to the capital, Damascus, and border crossings with Jordan.
The group said the battle for Sanamein killed at least 29 civilians, 16 rebels and nine pro-Assad troops, mostly in shelling and summary executions. It was not clear which side attacked the civilians.
A video posted online by opposition activists appeared to show the bodies laid out in a building, with children among the dead.
Elsewhere in Syria, rebels said that they shot down a government helicopter in the northern province of Idlib on Thursday as it tried to deliver supplies to an army base they have surrounded.
Another activist Internet video showed the gruesome aftermath of the helicopter's crash, with the bodies of its four-man crew sprawled around a field.
Charges of deliberate attacks
U.S.-based rights group Human Rights Watch said the Assad government also has used helicopters and fighter jets to carry out deliberate and indiscriminate attacks against civilians, killing more than 4,000 since the middle of last year.
In a report published Thursday, the group said the Syrian air strikes constitute war crimes and urged the international community to pressure Assad to stop them.
HRW Middle East and North Africa deputy director Nadim Houry told VOA the attacks also amount to crimes against humanity when carried out as part of a Syrian government policy.
"Many of the helicopters are using barrel bombs," said Houry. "These are makeshift bombs prepared by the Syrian air force sometimes on their bases, and they just drop these bombs from the back of the helicopter from very high places without any real targeting. So they are really punishing the civilian population in the areas where the opposition has taken control."
HRW said it sent a team into Syria between August and December, documenting 59 government air strikes on rebel areas of Aleppo, Idlib and Latakia. It said those attacks killed 152 civilians, some at bakeries and hospitals.
Houry said the impact of the air strikes goes beyond the immediate casualties.
"They are also affecting life in large parts of the country because people live in constant fear of what is going to happen," said Houry. "Many parents for example do not send their children to schools and have stopped lining up to buy bread at bakeries because of repeated air strikes. It is really creating a sense of terror, given the weapons being used by the Syrian air force including cluster munitions which are inherently indiscriminate."
In 41 of the air strikes documented by the team, HRW said rebel positions were located within 50 to 400 meters of where the government missiles hit civilians. Houry said opposition fighters should avoid that kind of proximity.
"Their violations are mostly tied to the fact that they have not taken all necessary precautions to protect civilians and minimize harm, for example by sometimes basing themselves in houses or buildings in civilian areas," said Houry. "But even these cases do not relieve the obligation of the attackers of the Syrian air force to take the necessary precaution to minimize harm to civilians, which is something that they clearly have not done."
The Syrian government had no immediate response to the HRW accusations. It has long claimed that it is fighting only against foreign-backed terrorists, denying the existence of the two-year revolt against Assad's autocratic rule.