Syria said its troops seized a rebel-held Aleppo district on Wednesday after storming it and \"annihilating\" most of the insurgents, as a long-threatened ground assault on the key city was launched. The claim was promptly denied by the rebels, who nonetheless acknowledged that a \"barbaric and savage attack\" on the neighbourhood of Salaheddin was under way. The offensive came as Amnesty International raised concerns about the plight of civilians in the commercial capital and warned both sides they would be held accountable for any attacks on its residential areas. State news agency SANA said \"our brave armed forces have taken full control of the district of Salaheddin\" and \"inflicted heavy losses on groups of armed terrorists, killing or wounding a large number of them.\" Dozens of rebels had been captured, including foreigners, and others had surrendered, SANA said, adding troops had also seized a large number of arms \"used by the terrorists to terrify the inhabitants and to murder members of the forces of order.\" For its part, state television said the \"armed forces dealt violent blows to the mercenary terrorists\" in Salaheddin, \"annihilating most of the terrorists.\" Reacting to those claims, Colonel Abdel Jabbar al-Oqaidi of the rebel Free Syrian Army said \"it is not true the regime army has seized control of the district.\" \"It is true that there is a barbaric and savage attack,\" he told AFP via Skype. \"They are using all the weapons at their disposal to attack Salaheddin, including fighter jets, tanks and mortars.\" He said there was fighting in many districts, but that it was concentrated in Saleheddin because of the \"great symbolic value for us and the army.\" A security official in Damascus said \"the elimination of pockets of resistance should continue until Thursday morning. The army\'s intention is then to seize the adjacent district of Seif al-Dawla, to the east.\" On Sunday, an official had said the army had massed 20,000 troops for the assault to recover Aleppo, of which the rebels claim they hold half. He said the insurgents had 6,000-8,000 men. Earlier, the Syrian Observatory for Human Rights said 16 civilians were killed in Aleppo and in the rest of the same province, with six more elsewhere in the country. A total of 225 people -- mostly civilians -- died in Syria on Tuesday. That made it one of the worst days for casualties in the 17-month uprising that the Observatory said last week had cost more than 21,000 lives. The neighbourhoods of Qatarji, Tariq al-Bab and Shaar also came under heavy shelling. The Syrian Revolution General Council, a network of activists on the ground, reported overnight shelling in the neighbourhoods of Al-Kalassa, Shaar, Sukari and Tariq al-Bab as well as heavy artillery fire aimed at the Bustan al-Qasr and Fardoss districts. In Lebanon, a dozen shells from the Syrian side of the border struck overnight, causing no casualties, a security official in northern Lebanon said. Amnesty showed satellite images indicating an apparent increased use of heavy weapons in the area, and warned forces loyal to President Bashar al-Assad attacks on civilians would not go unpunished. \"Amnesty International is sending a clear message to both sides in the fighting: Any attacks against civilians will be clearly documented so that those responsible can be held accountable,\" Amnesty\'s Christoph Koettl said. The London-based watchdog said images from Anadan, a small town near Aleppo, revealed more than 600 probable artillery impact craters from the fierce fighting over the city. It said an image from July 31 showed what seemed to be artillery impact craters next to what appeared to be a residential housing complex in Anadan. Amnesty said it was concerned the deployment of heavy weaponry in residential areas would lead to further human rights abuses and grave breaches of international law. On Tuesday, Assad vowed to crush the rebellion that erupted in March 2011. \"The Syrian people and their government are determined to purge the country of terrorists and to fight the terrorists without respite,\" he was quoted by state news agency SANA as telling a visiting Iranian envoy, using his regime\'s terminology for rebel fighters. Assad had earlier appeared on television for the first time in more than two weeks in a meeting with Saeed Jalili, a top aide to Iranian supreme leader Ayatollah Ali Khamenei. Jalili offered Assad his country\'s backing, saying Tehran would \"never allow the resistance axis -- of which Syria is an essential pillar -- to break. \"What is happening in Syria is not an internal issue but a conflict between the axis of resistance on the one hand, and the regional and global enemies of this axis on the other,\" he said. On Wednesday, Iranian Foreign Minister Ali Akbar Salehi said retired members of the Revolutionary Guards and army were among the 48 Iranians taken hostage in Syria by rebels. \"A number of the (hostages) are retired members of the Guards and the army. Some others were from other ministries,\" Salehi was quoted as telling reporters as he flew back from Turkey, which he asked for help in freeing the Iranians. It was the first time Tehran admitted any of those abducted had a connection to its military, having previously insisted the 48 Iranians were only pilgrims travelling to a Muslim holy site in Damascus. On Tuesday, Jordan\'s King Abdullah II said Assad might make a \"worst case scenario\" retreat to an Alawite stronghold if he falls from power. \"I have a feeling that if he can\'t rule Greater Syria, then maybe an Alawi enclave is Plan B,\" Abdullah said in an interview with US television network CBS. \"That means that everybody starts land grabbing which makes no sense to me. If Syria then implodes on itself that would create problems that would take decades for us to come back from.\" King Abdullah predicted Assad would keep up his brutal crackdown to cling to power because he \"believes that he is in the right.\"