Two UN envoys went to Damascus on Tuesday and Wednesday and held talks with Syria's deputy prime minister and foreign minister, read a brief UN statement.

"The discussions were thorough and productive and led to an agreement on

the way forward," added the statement, without giving any other detail.

Ake Sellstrom, the chief inspector in the UN investigation team, and Angela Kane, the UN high representative for disarmament, were to report to UN leader Ban Ki-moon on the trip.

Ban has demanded widespread access to investigate all allegations of the

use of chemical weapons in the 28-month-old conflict. Syria has insisted that the UN only investigate its claim that opposition rebels used chemical weapons in the town of Khan al-Assal on March 19.

The UN says it has received reports of 13 attacks in the conflict. Britain, France and the United States say all the attacks were carried out by President Bashar al-Assad's forces. Russia, Assad's main ally, says its inquiry found opposition rebels used sarin gas in Khan al-Assal.