Rebels seized control of sections of Syria’s international borders and torched the main police headquarters in the heart of old Damascus, advancing relentlessly after the assassination of President Bashar al-Assad’s closest lieutenants.The battle for parts of the capital raged into the early hours of Friday, with corpses piled in the streets. In some neighbourhoods, residents said there were signs the government’s presence was diminishing.Officials in neighbouring Iraq confirmed that Syrian rebels were now in control of the Syrian side of the main Abu Kamal border checkpoint on the Euphrates River highway, one of the major trade routes across the Middle East.Rebels also claimed control of at least two border crossings into Turkey at Bab al-Hawa and Jarablus, in what appeared to have been a coordinated campaign to seize Syria’s frontiers.In Damascus, a witness in the central old quarter district of Qanawat said the huge headquarters of the Damascus Province Police was black with smoke and abandoned after being torched and looted in a rebel attack."Three patrol cars came to the site and were hit by roadside bombs,” said activist Abu Rateb by telephone. "I saw three bodies in one car. Others said dozens of security men and shabbiha (pro-Assad militia) lay dead or wounded along Khaled bin al-Walid street, before ambulances took them away.”The next few days will be critical in determining whether Assad’s government can recover from the devastating blow of Wednesday’s bombing, which wiped out much of Assad’s command structure and destroyed his circle’s aura of invulnerability.Security chief dies from woundsSyria’s national security chief has died yesterday from injuries he received in a bomb attack in Damascus on Wednesday, state TV has announced.Assad’s powerful brother-in-law, his defence minister and a top general were killed in Wednesday’s attack. The head of intelligence and the interior minister were wounded.Hisham Ikhtiar is the fourth regime insider to die as a result of the attack at national security offices.Fighting is raging around Syria, with rebels seizing several border posts.Meanwhile, Russia’s envoy to France has sparked a row with Damascus after suggesting President Bashar al-Assad was ready to step down.Alexander Orlov said Mr Assad had, in effect, agreed to step down last month at a conference in Geneva which had planned for a democratic transition."Assad nominated his representative to lead the negotiations with the opposition for this transition. That means he accepted to leave, but in a civilised way,” said Mr Orlov.His comments triggered an angry response from Syria, where the information ministry said the claims were completely baseless.