DAMASCUS (AFP) - Syrian troops pushed towards the Lebanese border on Sunday as they pressed a deadly crackdown in central towns on the eve of an opposition meeting in Damascus on the country's unrest, activists said. The latest violence in Kseir, near the flashpoint city of Homs, forced "hundreds" of people to flee over the border into Lebanon, the activists said. The exodus came as Turkey, where about 12,000 Syrians have already taken refuge in recent weeks, scrambled to build a border tent city to accommodate a possible new influx of refugees. Rami Abdel Rahman, who heads the London-based Syrian Observatory for Human Rights, told AFP in Nicosia that shots rang out overnight in Kseir - 15 kilometres (nine miles) from the border with Lebanon, and in Homs. "Shots were heard overnight Saturday in the town of Kseir," he said quoting residents, adding that, further north, gunfire was heard in several Homs neighbourhoods. "Yesterday (Saturday) hundreds of residents fled from Kseir to Lebanon," Abdel Rahman said. Four civilians were shot dead by security forces on Saturday, two of them in Kseir and the other two in Kiswah, south of the capital. Activists say that security forces have bolstered their presence in Kseir since Friday, while troops have been controlling areas of Homs for several days, as part of a policy to crush pro-democracy protests. The sweep against the opponents of the autocratic regime of President Bashar al-Assad has also seen troops backed by tanks storm villages near the border with Turkey. On Saturday, tanks rumbled into Al-Najia, after similar operations in Jisr al-Shughur, seized on June 12, and Khirbet al-Joz, where troops deployed on Thursday, according to activists. Pro-government daily Al-Watan said Khirbet al-Joz was used as a "key crossing for armed groups from and to the Turkish" border.