The UN Security Council was to meet at 3:00 pm (1900 GMT) Wednesday over reports of a chemical weapons attack in Syria that allegedly killed hundreds, diplomats said.
UN Secretary General Ban Ki-moon's office said he was "shocked" by the reports of the attack and that UN inspectors in Syria to probe previous allegations were in discussions with Damascus.
Security Council members France, Britain, the United States, Luxembourg and South Korea requested the meeting, which was to be held in the form of closed-door consultations, a diplomat said.
Paris and London were to send a joint letter Wednesday to the secretary general asking him to order the team of UN experts in Syria to go to the scene to investigate.
The United States demanded that Syria provide immediate access to the site, while Russia, a close ally of the Syrian government, called the opposition claims a "provocation."
The main Syrian opposition group claims as many as 1,300 people were killed in a chemical weapons attack Wednesday on rebel areas near Damascus.
Videos distributed by activists, the authenticity of which could not immediately be verified, showed medics attending to suffocating children and hospitals being overwhelmed.
The objective of the Security Council consultations is to "take the temperature and to inform" the 15 members, but it was not expected to result in any formal position, a diplomat said.
The diplomat also said it would be difficult for the UN experts to investigate the incident because the alleged attack site was not one of three where the Syrian regime had agreed to UN inspections.
That means that the head of the UN experts in Syria, Ake Sellstrom of Sweden, must negotiate access to the new site with Syrian authorities, the diplomat said.
The UN statement said Sellstrom's team is "following the current situation in Syria carefully, and remains fully engaged in the investigation process that is mandated by the Secretary General.
"Professor Sellstrom is in discussions with the Syrian Government on all issues pertaining to the alleged use of chemical weapons, including this most recent reported incident."