Iran, an ally of Syrian President Bashar Al Assad, has sent mainly military experts to help him in his battle with rebels.
A mainstream Syrian rebel group said on Monday they were seeking to swap an Iranian taken captive in the southwestern province of Deraa last month for women held in Syrian government jails.
Iran, a Shi'ite Muslim ally of Syrian President Bashar Al Assad, has sent mainly military experts to help him in his almost four-year-long battle with mostly Sunni Muslim rebels.
Last month several insurgent groups including the Sham Unified Front launched a major offensive in the province of Deraa in which they seized several military posts including a strategic army base in the Sheikh Maskeen area.
The group's leader Abu Ahmad said his rebels captured the Iranian as he was fighting alongside government forces in the province, and killed nine other soldiers as they took over a power station near Sheikh Maskeen in the province.
"We questioned him through a translator, he came to Syria last year, he is a 30-year-old and he comes from (the Iranian) city of Qom," Abu Ahmad, who was not using his real name, told Reuters.
"We are questioning him on how Iranians operate in Syria. Our priority right now is a swap (of him) for our prisoners. We have so many women in government prisons and we want to swap him for (some) them."
Reuters could not independently verify the account.
The opposition has consistently demanded the release of thousands of women they say have been jailed for involvement in anti-government activism since March 2011, when the civil war began as peaceful street protests.
The Sham Unified Front is part of the Southern Front alliance of mainstream rebel groups operating near the border with Jordan where they have managed to seize positions from government forces and hold them.
Two years ago, Syrian insurgents freed 48 Iranians they held in exchange for more than 2,000 civilian prisoners held by the Syrian government.
Opposition groups accuse the government of detaining tens of thousands of prisoners in its attempt to crush the anti-Assad revolt in which radical Islamist rebels have increasingly predominated, seizing much of the north and east of Syria.
Iranians killed in Syria's war have included several retired generals from the elite Iranian Revolutionary Guards. A general in the Revolutionary Guards was killed by an Israeli air strike in southern Syria last month, together with six operatives of the Lebanese Shi'ite Hezbollah movement, an ally of Assad and Iran.