2130 opposition prisoners were released by the Syrian government in exchange for 48 Iranians abducted in Damascus, while apparently on a pilgrimage five months ago.
The swap is the first major swap of the 21-month long civil war and was brokered by a Turkish humanitarian group and the Qatari government.
Syrian opposition fighters alleged that the 48 prisoners were members of the Iranian revolutionary guard corps which was assisting Assad to crush the rebellion.
Iran denied the allegations although admitted that some of the detainees were retired guards.
See here for full report on the Guardian.