Nearly 50 soldiers and rebels were killed on Saturday in clashes near Syria's northern border, as Turkey hit back against what it said was new mortar fire from inside Syria.
Damascus, for its part, said four Turks were among a convoy of "terrorists" killed in the heart of Aleppo, just hours after UN condemnation of deadly jihadist bombings in the country's commercial capital.
Forty government soldiers and nine rebels were killed when rebels took a town in the northwestern province of Idlib near the border, the Syrian Observatory for Human Rights said.
"The clashes at Khirbat al-Joz... ended when fighters of the rebel brigades took control of the area," said the Britain-based watchdog.
"The fighting lasted more than 12 hours and resulted in at least 40 dead among the regular forces, including five officers, and nine (rebel) fighters," it added after earlier reporting 25 soldiers and three rebels dead.
Turkish officials said they were sure a mortar round that struck on Saturday morning was fired by pro-government forces in Syria, and not rebels who have been fighting for nearly 19 months to oust President Bashar al-Assad.
It prompted fresh retaliatory fire after reprisals on Wednesday and Thursday for the previous shelling, the Hatay provincial governor's office said.
"A mortar round struck today (Saturday) at 7:00 am (0400 GMT) about 50 metres (yards) inside Turkish territory in an open space about 700 metres from the village of Guvecci and about 300 metres from a police station."
No casualties were reported.
The Turkish army responded with four mortar rounds, the governor's office said, adding that the Syrian fire had come from loyalists who were firing at rebels near the border.
The cross-border exchanges came despite unanimous condemnation from the UN Security Council on Thursday of deadly shelling from the Syrian side further east in Sanliurfa province that killed five people.
Following that incident, the Turkish parliament authorised further military action but Prime Minister Recep Tayyip Erdogan said he was not seeking a mandate for war.
In a new statement on Friday, the Security Council condemned bombings Wednesday claimed by a jihadist group that killed nearly 50 people in Aleppo, expressing condolences to families of the victims "of these heinous acts."
State television, meanwhile, said four Turks were among foreign fighters the army had killed in the Bustan al-Qasr district of the battleground city of Aleppo.
"Our valiant forces destroyed two vehicles fitted with Dushka (anti-aircraft heavy) machineguns and seven Mercedes with the terrorists inside, including four Turks," it said.
Syria has repeatedly complained that it is fighting armed terrorists supported from abroad.
Iran's foreign ministry on Saturday appealed for Turkish help in securing the release of 48 of its citizens held by rebels in Syria and threatened with execution unless the army withdraws from an area in Damascus province.
In Damascus, Assad laid a wreath at the tomb of the unknown soldier to mark the anniversary of the 1973 Arab-Israeli war.
State television carried pictures of the president at the monument on Mount Kassioun on the outskirts of the capital.
Defence Minister General Fahd al-Freij told state television victory was near for his forces and said repentant rebels would be welcomed back.
"Commanders of the army are determined to restore security in our Syria. Victory is near," he said. "The fatherland opens its arms to all our children, including those who have committed errors and want to return to the fold."
Meanwhile, Mokhtar Lamani, the head of UN-Arab League peace envoy Lakhdar Brahimi's office in Syria, met rebel members on Saturday, a UN official told AFP.
Lamani visited the Jat area some 50 kilometres (30 miles) south of Damascus and "met leaders of the armed opposition," spokesman Khaled al-Masri said, as part of contacts with all parties in the conflict.
In the north, fighting was reported on the outskirts of the Tareq al-Baba district of Aleppo.
"I've never seen so many rebels in the area. They've put mortars on the rooftops and municipal buses at the entrances to Tareq al-Bab to keep out the army," said one resident.
Nationwide, at least 88 people were killed on Saturday -- 38 soldiers, 32 rebels and 18 civilians -- according to the Observatory, which gave a death toll of 133 for Friday.
Since the uprising against Assad's rule erupted in March last year, more than 31,000 people have been killed, according to the group.
In other developments, a Russian aid plane flew in to Damascus on Saturday with 24 tonnes of medicine and medical supplies, Syria's official news agency SANA said.