A top UN envoy said Wednesday there are "mounting reports" of the use of chemical weapons in Syria's civil war and called on the Damascus government to let in UN investigators.
The United Nations has been alerted to new chemical weapons since the start of April, according to diplomats.
UN leader Ban Ki-moon "remains gravely concerned about the allegations of the use of chemical weapons" in the 26-month-old conflict, UN special envoy on the Middle East peace process Robert Serry said.
"Amid mounting reports on the use of chemical weapons, we once again urge the government of Syria to allow the investigation to proceed without further delay," Serry told the UN Security Council.
Serry did not give detail of the new reports. But Western nations have passed on details of new allegations, diplomats said.
"We continue to get information about new incidents and we will continue to pass those to the secretary general," said one Western diplomat.
The diplomat, who spoke on condition of anonymity, also gave no detail, but said the alleged attacks had occurred "since the beginning of April."
President Bashar al-Assad's government called for a UN investigation but has blocked UN experts who have called for access to all parts of the country so that they can look into opposition claims as well.
Syria has insisted that any investigation be limited to government claims that opposition rebels fired chemical weapon shells at Khan al-Assal, near Aleppo, on March 23 when more than 30 people reportedly died.
Following official requests by Britain and France, Ban has demanded that the experts also investigate the alleged use of the weapons at Homs in December.
Turkey's Prime Minister Recep Tayyip Erdogan said on May 10 that Syrians showing signs of chemical attacks had been brought to hospitals in Turkey, and that "remainders of missiles" that he believes were used in such attacks have been found.
Foreign Minister Ahmet Davutoglu added that authorities were conducting blood tests on wounded Syrian refugees to assess whether their injuries had been caused by chemical weapons.
Turkish authorities have not said, however, when the suspected attacks were staged.
The US administration said on May 15 that it believed small amounts of chemical weapons had been used at least twice in Syria but that it was awaiting full confirmation.
A team of UN experts led by Swedish scientist Ake Sellstrom is already studying evidence brought out of Syria. Serry said the team was continuing its work.