A standoff loomed Sunday between Syrian rebels and government forces near Aleppo as the battle for control of the most populous city intensified and the regime deployed heavy weapons to drive out the fighters. Government artillery and helicopter gunships pounded rebel positions, according to opposition activists. "The buzzing of the warplanes don't stop," said Bashir Al-Hajji, a spokesman for a Free Syrian Army brigade in Aleppo. "But we already started to move forward from the eastern neighborhoods and God willing, the fight will be over soon and we will be victorious." Al-Hajji said clashes have raged for hours at various spots near the Aleppo city center, including close to the presidential palace. He said he is in the Industrial City of Aleppo, about 15 kilometers (9 miles) from the city of Aleppo, which is the commercial capital. Rebel fighters said they have surrounded the highest point in Aleppo, where regime forces are holed up. Two large columns of government troops are heading toward the city, according to Free Syrian Army fighters. Members of the Free Syrian Army are trying to stop the approaching troops by attacking them in Idlib province, said Mohamed Said, an Aleppo spokesman for the Syrian Revolution General Commission. As rebels scrambled to fend off regime forces in Aleppo, more gunfire erupted in other parts of Syria, with at least 26 killed nationwide Sunday, the opposition Local Coordination Committees said. The deaths incluced three executions in the Damascus area and six executions in Aleppo, the group said. United Nations Secretary-General Ban Ki-moon said the situation may get worse in Aleppo, describing it as "the epicenter of a vicious battle between the Syrian government and those who wish to replace it." Rebels in Aleppo exude gritty confidence and possess growing clout. They say they are in charge of significant parts of the city and are working to wrest control of the entire sprawling metropolis from the better-equipped forces of Syrian President Bashar al-Assad. The regime reported deaths, injuries and the capture of "terrorists" -- who Syria has consistently said are behind attacks -- in several neighborhoods of Aleppo on Saturday. Opposition activists, meanwhile, said al-Assad's forces had unleashed persistent and powerful bombs and shelling, while rebels have launched their own attacks in multiple neighborhoods. That includes a brazen push Friday to seize a state-run broadcasting building in Aleppo. Rebels pushed into the radio and TV complex, and took over parts of it, before eventually withdrawing because of snipers and military shelling, the opposition Local Coordination Committees of Syria said. Syria's civil war is hardly confined to Aleppo. On state TV, Syrian President Bashar al-Assad's regime said dozens of "terrorists" were killed or injured in an explosion at an ammunition and improvised explosive device storage site in Homs. Around Syria's capital, "armed terrorists" attacked a bus carrying 48 Iranian Shiite pilgrims and kidnapped them, Iranian state media said. Syrian state media also reported the abduction and said it is under investigation. It is unclear whether the hijacking is linked to the uprising against the Syrian government. The Iranian government is an ally of the al-Assad regime, which has been fighting a rebel movement dominated by Sunnis. Iran is asking Turkey to step in to help free the pilgrims, according to IRNA, Tehran's state media. In a phone call to his Turkish counterpart, Foreign Minister Ali Akbar Salehi asked for "prompt intervention of Ankara" to help release the pilgrims, IRNA said Saturday. Turkey has tense relations with the Syrian regime and is sympathetic to the rebels. Television network Al Arabiya aired video purporting to show the pilgrims detained by Syrian rebels. In the video, a commander of the Free Syrian Army says the 48 people abducted are revolutionary guards and not pilgrims. CNN cannot independently verify the authenticity of the video. Roughly 17,000 people have died since the Syrian conflict first flared in March 2011, when government forces began cracking down on protesters, Ban said last month. Opposition activists put the toll at more than 20,000. The violence has intensified during the Islamic holy month of Ramadan, which began July 21 in Syria and ends this month, the Red Cross said. Meanwhile, the Syrian envoy to the United Nations, Bashar al-Jaafari, said his family received numerous death threats in the United States. He has reported the threats to U.S. officials, according to Syrian state media. Hillary Clinton plans to visit Turkey on Saturday to discuss the Syrian crisis, the State Department said.