* Iran says slain commander worked on Lebanon reconstruction
* Rebels take town in eastern oil producing province
* Fighters shoot down two air force jets -monitoring group
By Dominic Evans and Mariam Karouny
BEIRUT, Feb 14 (Reuters) - An Iranian military commander has been killed in Syria by rebels fighting Tehran's ally President Bashar al-Assad, Iran said on Thursday, describing the dead man as a Revolutionary Guard.
The rebels accuse the elite corps of sending forces to help Assad crush their 22-month-old uprising - a charge denied by the Islamic republic, whose Shi'ite form of the religion is anathema to many of the Sunni Muslim rebels battling to topple Assad.
The Iranian embassy in Beirut named the man as Hessam Khoshnevis and said he ran Tehran's reconstruction aid programme for Lebanon. It said he was killed by "armed terrorist groups", a label used by the Syrian government to describe Assad's foes, on the highway as he returned to Lebanon from Damascus.
There were contradictory accounts of when that happened; Iran said it was on Tuesday but, after statements by Iranian officials, various Syrian rebel groups offered divergent accounts of him being killed by them as long ago as last month. One force said he died during an Israeli air strike on Jan. 30.
Iran has strongly backed Assad during the uprising in which the United Nations says nearly 70,000 people have been killed. In September, the Revolutionary Guards commander-in-chief said his force was providing non-military support in Syria and might get involved militarily if there were foreign intervention.
Syria, where Assad's Alawite minority is an offshoot of Shi'ite Islam and the majority of the population is Sunni, has become a proxy battleground for a regional confrontation between non-Arab Iran and Sunni-ruled Arab powers, such as Saudi Arabia.
Last year, Syrian rebels kidnapped 48 Iranians whom they accused of being Revolutionary Guards fighters while authorities in Tehran insisted they were pilgrims. The men were freed this year in a prisoner swap with Syrian authorities.
Details of Khoshnevis's killing, which Iranian news agencies said happened on Tuesday, were sketchy and Iran's envoy to Beirut drew a link with Israel.
"He served the oppressed, supporting the resistance to Israel," Ghazanfar Roknabadi said. "Assassinating this dear martyr is a clear sign that the Zionist enemy does not accept his successful work".
The Free Syrian Army said he died in an Israeli air strike last month on a Syrian military centre outside Damascus, while other rebels said he was killed near the border town of Zabadani this week - or in an attack on a convoy three weeks ago.
In Tehran, a funeral service was held for Khoshnevis on Thursday, Iran's semi-official Fars news agency reported, attended by senior Revolutionary Guards commanders.
TEHRAN BACKS ASSAD
The Revolutionary Guards media office said Khoshnevis would be buried in his home town of Semnan after being "martyred on his way from Damascus to Beirut by mercenaries".
Tehran's IRNA news agency said Khoshnevis, identified in some reports as Commander Hassan Shateri, was a military engineer during the 1980-88 conflict between Iran and Iraq, and had later worked in Afghanistan.
Officials stressed Khoshnevis had been engaged in civilian reconstruction in Lebanon for the last seven years. Iran backs the Lebanese Shi'ite movement Hezbollah, which fought a brief war with Israel seven years ago.
Lebanon's Al-Safir newspaper said Khoshnevis was in Syria to study reconstruction plans for the northern city of Aleppo.
Whole districts of Aleppo, Syria's largest city, and other urban centres across the country, have been destroyed in months of entrenched urban warfare.
Activists said rebels shot down two air force jets in the northern Syrian province of Idlib on Thursday. There has been fierce fighting in the province in the last week around the Wadi Deif military base, close to the main north-south highway.
Rebels also said they captured the town of Shaddadeh in the eastern, oil-producing province of Hasakah after three days of battles in which, they said, 30 members of the al Qaeda-linked, anti-Assad, Nusra Front and 100 soldiers were killed.
Taking Shaddadeh brings the rebels closer to the provincial capital Hasakah, 45 km (30 miles) to the north.
Omar Abu Laila of the FSA's eastern command said an army garrison guarding a nearby gas field, al-Ghabsa, had fled as the rebels advanced from the Euphrates river toward Shaddadeh.
"Shaddadeh and Ghabsa are now under our out control. In the next few days we will advance toward the city of Hasakah," Abu Laila said by telephone from eastern Syria.
But the rebel gains to the east were offset by advances by Assad's forces around Homs, the country's third biggest city and a vital link between Assad's power base in Damascus and the heartland of his Alawite community near the Mediterranean coast.
Activists in Homs said the army moved into the southwestern districts of Jobar and Soltaniyah on Wednesday night after heavy bombardment of the two neighbourhoods this month. Soldiers have also taken two districts to the northeast of the city, tightening their encirclement of remaining rebel-held areas in the centre which have been under siege for months.
"We feel that our time is coming, and we are next. But we don't have anywhere to go," a resident of the central Khalidiyah neighbourhood of Homs told Reuters.
In the southern province of Deraa, cradle of the protests which erupted against Assad in March 2011, rebels said they broke into one of three military bases from which Assad's forces have shelled targets in the east of the province.
They posted videos on the Internet of fighters firing from behind trees, entering the base and seizing at least two tanks.
Near Damascus, opposition sources said, rebels launched a counter-offensive against positions manned by troops and pro-Assad militia in the suburb of Daraya and other areas near the city's ring road, scene of fierce fighting in the last few days. (Additional reporting by Khaled Yacoub Oweis and Suleiman al-Khalidi in Amman and Zahra Hosseinian; Editing by Alastair Macdonald)