DAMASCUS, Syria - Syria accused neighboring Turkey Sunday of allowing thousands of Muslim extremists to cross into its territory, as the government and opposition said an explosion killed at least seven and cut off a main road leading south from the capital.
In letters to the U.N. Security Council and Secretary-General Ban Ki-Moon, Syria's Foreign Ministry said Turkey allowed "thousands of al-Qaida, Takfiri and Wahhabi terrorists" access to the country in order to "kill innocent Syrians, blow up their properties and spread chaos and destruction."
Syrian authorities blame the anti-government uprising that began in March last year on a foreign conspiracy and accuse Gulf countries Saudi Arabia and Qatar, along with the U.S, other Western countries and Turkey, of offering funding and training to the rebels, whom they describe as "terrorists."
Turkey serves as headquarters for the leaders of the Free Syrian Army rebels and hosts many meetings of the Syrian National Council opposition group. Relations between Turkey and Syria, once strong allies, have been deteriorating since after the crisis began last year and Ankara became one of President Bashar Assad's harshest critics.
Although the conflict has left Syria internationally isolated, Iran has stood by Assad.
On Sunday, the top commander of Iran's powerful Revolutionary Guard says the elite unit has high-level advisers in Lebanon and Syria but remains undecided on whether to send military reinforcements to help save Assad's regime.
Sunday's comments by Gen. Mohammad Ali Jafari were the clearest indication to date of Iran's direct assistance to its main Arab allies, Assad and Lebanon's Hezbollah. It also suggests Tehran is wary about being drawn into a Middle East conflict if outside forces attack Assad, who is locked in a civil war with rebel forces.
Jafari told reporters that Quds force members have been in Syria and Lebanon as advisers for a long time, but was not more specific.
He said decisions about whether to boost military aid to Syria if attacked would "depend on the circumstances."
Also Sunday, state-run news agency SANA said rebels detonated a 600 kilogram (1,320 pound) bomb under the highway near the southern town of Khirbet Ghazaleh. It said the bomb was detonated by remote control and cut the highway that links Damascus with the southern city of Daraa and the Jordanian capital of Amman.
The opposition Local Coordination Committees said seven people were killed and others wounded, although SANA put the toll at eight. SANA added that nine cars and two buses carrying state employees were damaged in the blast.
Residents in the province of Daraa reported Sunday that government troops have been surrounding hamlets in the region. They said the "troops are not allowing people to leave their area, not even to go to school." One, who identified himself as Abu Wassim, said his elementary-aged sons could not attend classes on the first day of school in the country.
Other residents said the Syrian military was inspecting houses and randomly arresting people in the province. They alleged the troops were insulting and beating, particularly young men, during the inspections. Also, they reported receiving threatening text messages on their mobile phones warning: "Armed people, hand yourselves in because our intrepid army is coming to get you."
Earlier in the day, government troops captured and cleared the neighborhood of Midan in the embattled northern city of Aleppo, SANA said, while activists reported that bombardment of rebel-held areas throughout the country claimed the lives of dozens of people.
SANA said troops also killed dozens of rebels in other parts of Aleppo, the country's largest city and commercial center. The LCC and the Britain-based Syrian Observatory for Human Rights said many of the dead in Aleppo were killed in air raids on the rebel-held neighborhood of Shaar.
The fight for Aleppo, a city of 3 million that was once a bastion of support for Assad, is critical for both the regime and the opposition. Its fall would give the opposition a major strategic victory with a stronghold in the north near the Turkish border. A rebel defeat, at the very least, would buy Assad more time.
The Observatory also said troops shelled the Damascus neighborhood of Hajar Aswad, an area that has witnessed anti-government activities since the early weeks of the uprising.
Sunday's countrywide death toll reached over 50 people, the Observatory added. It was the same day that the school year began for some five million students.
The Syrian uprising began with mostly peaceful protests in a number of the country's impoverished provinces. As security forces violently suppressed them, the protest grew and escalated into an increasingly armed insurrection. Activists say at least 23,000 people have been killed in the past 18 months.
On Sunday, the new international envoy tasked with ending the civil war, Lakhdar Brahimi, left Syria, ending a four-day visit during which he met with Assad and other officials, his office said in a statement. Brahimi summed up his first foray to Damascus Saturday with a startling and frank admission that he still has no plan for stopping the bloodshed which he warned could threaten world peace.
In Damascus, some 24 political parties and groups who describe themselves as opposition organizations gathered in an effort to seek national reconciliation and end violence in the country.
The participants, who included Deputy Prime Minister Qadri Jamil - head the opposition party Front of Change and Liberation, said in a statement that they aim to launch a pure Syrian dialogue and call for a national conference to be attended by all opposition groups from inside and outside the country.