UN chief Ban Ki-Moon on Tuesday called on Syria to approve a United Nations mission of inspectors that would probe two alleged incidents of use of chemical weapons in the country's conflict.
"I appeal to the government of Syria to extend its full cooperation and to allow the mission to proceed," Ban told reporters in Rome.
Ban said the initial focus for the mission had been an incident in the village of Khan al-Assal on 19 March but that this had changed.
"Based on the information available to me, I have concluded that the mission should also investigate the allegation on the use of chemical weapons in Homs on 23 December," he said.
"I regret that the government of Syria has not yet agreed to the modalities I have proposed," he said.
Ban had said on Monday that a UN team was in Cyprus and ready to deploy to nearby Syria to investigate the alleged use of chemical weapons.
Damascus had asked for the investigation into its allegation that the opposition had used chemical weapons in Khan al-Assal, while rebels charged that government forces had deployed the munitions.
However, later on Monday, a Syrian foreign ministry official cited by state news agency SANA rejected the inspection as proposed by Ban.
He said that Syria "can not accept such manoeuvres on the part of the UN secretariat general, bearing in mind the negative role that it played in Iraq and which cleared the way to the American invasion" of that country in 2003.
The official said Syria had specifically requested "a neutral and honest technical team to visit the village of Khan al-Assal" in the northern province of Aleppo.
Ban has "suggested a supplementary mission allowing the mission to deploy throughout Syrian territory, which is contrary to the demand Syria made to the United Nations," the official said.
A UN source in Cyprus said the team leader, Swedish scientist Ake Sellstrom, left the island on Tuesday and the rest were expected to follow on Thursday.