Moscow - Russian news agencies denied reports that a Russian general had been killed in Syria and said he had appeared in person on Wednesday at the Defence Ministry in Moscow, reported Reuters.
The ministry said reports that a Russian general advising Syria's military had been killed amounted to a "bald-faced lie".
Itar-Tass news agency said a reserve officer called Vladimir Kuzheyev had later met Russian journalists at the ministry and, although he did not say whether he had been in Syria, he declared: "I want to confirm that I am alive and well."
Meanwhile, AFP reported on Wednesday that Syrian tanks stormed a rebel-held district of Aleppo, sparking fierce clashes that a security official said marked the start of a long-threatened ground assault on the key battleground city.
The assault on the country's commercial capital came as Amnesty International raised concerns about the plight of civilians in the city and warned both sides they would be held accountable for any attacks on civilians.
"The assault has genuinely begun," the security official in Damascus told AFP.
20 000 troops
"The army is advancing to cut [the southwestern rebel redoubt of] Salaheddin in two. It will not take long, even if there are still some pockets of resistance."
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.
Wassel Ayub, a commander of the rebel Free Syrian Army, said "regime forces advanced into Al-Malaab Street [in Salaheddin] with tanks and armoured vehicles, and fierce fighting is now taking place in the area".
A rebel commander said his men were being prevented from mounting a counter-attack by snipers.
The army first shelled several districts of the northwestern city before dawn.
Sixteen civilians were killed in Aleppo and in the rest of the same province, with six more elsewhere in the country, the Syrian Observatory for Human Rights said.
Worst day for casualties
Among the dead were a woman and her two children, killed when a shell struck their house in Al-Mashatiyah neighbourhood, the Observatory said.
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 International showed satellite images indicating an apparent increased use of heavy weapons in the area.
It warned forces loyal to President Bashar Assad that 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 31 July 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.
Worst case scenario
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".