The UN has reached a deal with Syria, allowing it to question witnesses in the probe into the killing of former Lebanese Prime Minister Rafik Hariri.
Lebanese supporters of Hariri continue to demand justice
The agreement on legal procedures was reached during talks between chief UN investigator Detlev Mehlis in Damascus, Syrian officials said.
Damascus, which denies any role in Hariri's assassination, has said that UN investigators are welcome.
Many in Lebanon have blamed Syria for February's killing of Hariri.
Mr Mehlis and a legal advisor from Syria's foreign ministry had agreed "on the measures and preparations for hearing the Syrian witnesses," a Syrian official told the state news agency, Sana.
The official added that Mr Mehlis would return to Damascus "at the end of next week".
Nothing has been said yet in Damascus about the identity of the witnesses, where Mr Mehlis will meet them and under what conditions.
But Lebanese media has been reporting that Mr Mehlis wants to speak to Rustom Ghazaleh, Syria's intelligence chief in Lebanon at the time of the assassination, as well as two of his aides.
The German prosecutor is also said to want to interview Mr Ghazaleh's predecessor, Jhazi Kanann, now the minister of interior, says the BBC's Kim Ghattas in Damascus.
The pressure on Damascus intensified after the arrest in Lebanon 10 days ago of four security chiefs, all top Syrian allies who were then charged with the murder of Hariri.
Syria maintains it was not involved in a killing. But it is likely that Mr Mehlis will try to find out the exact nature of the relationship between the four generals arrested in Lebanon and the Syrian intelligence chiefs, our correspondent says.
She says that Mr Mehlis may also want to speak to Syrian President Bashar al-Assad to clarify allegations that he threatened Hariri with physical harm during their last meeting more than a year ago.
Syria had 15,000 troops on Lebanese soil at the time of the 14 February assassination in Beirut.