BEIRUT/Moscow - Abdel Qader Saleh, the charismatic chief of the Syrian rebel Liwa al-Tawhid Brigade, has died of his wounds after a regime air strike last week, rebels and activists said Monday.

His death is a blow to the opposition, particularly in the Aleppo area that Saleh came from and fought in, where the Syrian regime has made a string of advances in recent weeks. Saleh was considered one of the opposition's most respected commanders, with ties across the opposition seeking to oust President Bashar al-Assad, and his death was widely mourned on Monday. The 33-year-old "was the first to organise peaceful demonstrations in Aleppo and then the first to attack the bastions of Assad's gangs", the opposition National Coalition said in a statement. "He became a living symbol in the hearts of the Syrians," the statement added.

Saleh's death was announced by Liwa al-Tawhid on its official Facebook page and confirmed by the Britain-based Syrian Observatory for Human Rights.

"Abdel Qader Saleh, known as Hajji Marea, died of wounds he sustained last Thursday when warplanes targeted the Liwa al-Tawhid leadership," the watchdog said in a statement. "He was taken to Turkey after being wounded, and died in a hospital there before being brought back to Syria for burial," Observatory director Rami Abdel Rahman told AFP.

Thursday's strike also killed Liwa al-Tawhid's intelligence chief Yussef al-Abbas, known as Abu al-Tayyeb.

He had been in a car along with Saleh, and another senior figure in the rebel group, Abdelaziz Salameh, who was also wounded. Following the attack, Liwa al-Tawhid arrested 30 people suspected of being regime informers. Saleh, chief of operations for Liwa al-Tawhid, was widely seen as the brigade's most important figure. A Syrian regime team held closed-door consultations in Moscow on Monday amid burgeoning Russian efforts to flex its diplomatic muscle and help set up elusive peace talks with the opposition. President Bashar al-Assad's envoys entered Moscow's Stalin-era foreign ministry skyscraper just as UN chief Ban Ki-moon disclosed in Vilnius that he hoped to convene the so-called Geneva II conference in mid-December.

The latest push for peace came amid uninterrupted fighting that saw a top rebel commander die of wounds suffered in a regime air strike and continuing army advances in the flashpoint northern city of Aleppo. The consultations in Moscow between the Syrian delegation and Russian Deputy Foreign Ministers Gennady Gatilov and Mikhail Bogdanov came just days after President Vladimir Putin held his first telephone talks with Assad in more than two years. The Kremlin said that Putin on Monday also discussed Syrian peace initiatives with Iranian President Hassan Rouhani. "Having examined the situation around Syria in detail, (Putin and Rouhani) confirmed their commitment to a peaceful solution to the conflict and noted the importance of efforts to prepare the international Geneva II conference," the Kremlin said in a statement.

Russia has been one of the Syrian regime's most important allies by providing it with diplomatic backing at the United Nations and supplying its forces with heavy weapons throughout the 32-month war.

But Moscow has also assumed an increasingly important role in recent diplomatic negotiations after successfully averting US air strikes in September by having Assad agree to a Russia-US plan to strip him of his chemical arms.

Russia has also invited rebel groups to Moscow for talks it hopes will minimise the differences among them and enable them to agree to unconditional peace negotiations in Geneva.

The Russian foreign ministry issued no immediate statement on the outcome of Monday's meeting with Assad's envoys and the Syrian team left the building without speaking to the press.

It remained unclear if Assad's representatives would be holding further meetings during their stay in Moscow or how long their visit would last.

The Syrian opposition said that Russia had also invited National Coalition president Ahmed Jarba for a three-day visit starting Monday that coincides with the visit of the regime officials.

Jarba's adviser Munzer Aqbiq told AFP on Sunday that the opposition head was interested in the invitation but regretted being unable to visit Moscow on Monday due to "preset official commitments".

UN chief targets mid-December talks

The Geneva II conference - meant to bring government and rebel representatives to the negotiating table for the first time - has been delayed for months because of seemingly-unreconcilable differences over the terms of the talks.

The opposition Coalition has agreed to attend the conference only if it leads to a transitional period that would see Assad's departure from power.

Both Russia and Syria's regime have rejected the demand. Moscow also want to see Syrian ally Iran join the negotiations - a condition rejected by Western states.

But UN leader Ban struck a relatively optimistic note on Monday while on a visit to Lithuania.

"I am not able to announce at this time any date. Our target is mid-December," Ban told reporters.

He said UN-Arab League envoy Lakhdar Brahimi would try to set the date in a meeting with Russian and US representatives in Geneva on November 25.

"They will review and, if possible, I hope that they will be able to set a date so that I can issue a statement," Ban said.

A Syrian newspaper had last week suggested that the conference would be held on December 12.