The Syrian army kept up its bombardment of rebel neighborhoods of the central city of Homs on Monday, activists said, after 79 people were killed in violence across the country the previous day.

Thirty-eight civilians, six of them children, were among Sunday's dead, the Syrian Observatory for Human Rights said. The violence also claimed the lives of 13 rebel fighters and 28 government troops, the Britain-based watchdog added.

Syria-based rebel fighters and activists said they would boycott an opposition meeting in Cairo on Monday, denouncing it as a "conspiracy" that served the policy goals of Damascus allies Moscow and Tehran.

The two-day meeting, to be attended by the main exiled opposition bloc, the Syrian National Council, and other smaller groups, is intended to forge a common vision for a political transition in Syria after 16 months of bloodshed.

Interior Minister Marwan Charbel revealed on Monday that an Internal Security Forces officer and a delegation of Salafist clerics visited Turkey to follow up the efforts underway to release 11 Lebanese Shiite pilgrims kidnapped in Syria in May.

In remarks to Voice of Lebanon radio (93.3), Charbel said the ISF officials and the Salafist Sheikhs went to Ankara to follow up with Turkish authorities the case of the 11 men.

Violence across Syria killed at least 43 people on Sunday, 36 of them civilians caught in fierce fighting between troops and armed insurgents.

Sunday's highest concentration of deaths was in the eastern province of Deir Ezzor where nine civilians and three rebels were reportedly killed.

Turkey scrambled fighter jets after Syrian helicopters flew close to the border, the army said Sunday, hiking tensions following last month's downing of a Turkish plane.

Four F-16 warplanes took off from Incirlik airbase in southern Turkey after Syrian helicopters flew four miles closer to the border than is normal, the statement said.

Iran on Sunday said weekend talks held between major powers seeking a solution to the conflict in Syria were "unsuccessful" because it and Syria were excluded.

"This meeting was unsuccessful... because Syria was not present and some influential nations were not present," Deputy Foreign Minister for Arab-African Affairs Hossein Amir Abdolahian told state television.

Russian technicians were involved in the taking down of the Turkish fighter jet by the Syrian military last week, the Sunday Times reported on Sunday.

Quoting Middle Eastern diplomatic sources, the Times reported that the decision to down the Turkish jet was intended to signal a warning to NATO to stay out of the conflict raging in Syria for over a year.

Turkey's military insisted Sunday that a jet fighter shot down by Syrian forces on June 22 was in international airspace, and not inside Syria, as claimed in a newspaper report citing U.S. intelligence.

The Turkish F-4 Phantom "was downed over the eastern Mediterranean in international airspace ... while it was flying solo and unarmed, and testing our existing radars' performance in the region," the army's general staff said in a statement posted on its website.

Both official media and an opposition group on Sunday branded as a failure a world powers deal on a transition plan for Syria a day after at least 120 people were reported killed in violence nationwide.

World powers meeting in Geneva on Saturday agreed a transition plan that could include current regime members, but the West did not see any role for President Bashar Assad in a new unity government.

At least 21 people were killed in fighting across Syria on Sunday, a watchdog said, with rebels and regime troops clashing in several provinces as they battled for control of restive areas.

Regime forces shelled several areas of Damascus province, a day after mortar fire killed at least 30 civilians attending a funeral in the town of Zamalka, 10 kilometers (six miles) east of the capital, according to the Syrian Observatory for Human Rights.