AMMAN, July 29 (Reuters) - Syrian rebels waged a spate of mortar attacks on Syrian army checkpoints in the southern province of Deraa in the biggest flare-up of violence since government forces retook the restive region three years ago, rebels, residents and the army said on Thursday. The widespread attacks at army outposts near the Damascus-Deraa highway leading to the border crossing of Nassib with Jordan also disrupted passenger and commercial traffic at the main gateway for goods from Lebanon and Syria to the Gulf. Multiple army checkpoints around key towns and villages from the town of Nawa north of the province to Muzarib near the border with Jordan were also seized, they said. The army has sent reinforcements from its elite Fourth Division, run by Syrian President Bashar al-Assad"s brother Maher, senior military defectors said, confirming army leaks. The attacks came after the army launched a dawn operation against the rebel-held old quarter of the city of Deraa, where peaceful protests against decades of autocratic Assad family rule began in 2011 and were met by deadly force before spreading across the country. The army has sought to reassert its control after the collapse of talks earlier this week to get local elders and former rebels to allow the army to extend its control inside the old quarter, known as Deraa al Balad. The Syrian army, aided by Russian air power and Iranian militias, retook control of the strategic province that borders Jordan and Israel"s Golan Heights to the west in the summer of 2018. Russian-brokered deals at the time forced rebels to hand over heavy weapons and return state institutions in the enclave but kept away the army from entering their neighbourhoods. "The rebels have waged a counter offensive after the army operation against Deraa whose intensity has taken the regime by surprise," said Zaid al Rayes, a political opposition figure in touch with local groups in Deraa. State media said terrorists had fired at the main hospital in Deraa and the army had evacuated hundreds of fleeing families from rebel held neighbourhoods. Thousands of former rebels had chosen to stay with their families rather than head to remaining rebel-held areas in northern Syria, where tens of thousands of others displaced from recaptured areas had gathered. The province saw a widespread boycott of last May"s polls that extended Assad"s presidency in what officials saw as a defiance of state authority. Western intelligence sources say growing dissent is aggravated by the presence of Iranian-backed local militias who now hold sway and act with impunity since the central government is too weak to impose its authority on the area.