The UN Security Council met Wednesday over reports of a chemical weapons attack in Syria that the opposition says was carried out by the army and killed more than 1,300 people.
UN Secretary General Ban Ki-moon's office said he was "shocked" by the reports and that UN weapons experts 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 held behind closed doors.
Several council members including the United States and France have asked that the team of UN inspectors be dispatched immediately to the scene to investigate.
Washington demanded that Syria provide immediate access to the site, while Russia, a close ally of the Syrian government, called the opposition claims a "provocation."
Britain, France, Germany and the United States sent a formal request for an investigation of the incident to Ban's office.
Diplomats said the joint letter cited "credible reports of the use of chemical weapons."
"We urge you to do all you can to ensure that the mission has urgent access to all relevant sites and sources of information," the letter said.
As he headed into the meeting, Pakistani UN envoy Masood Khan said his country supported such an inquiry, but refused to speculate on the outcome of the meeting.
"We will see. We will have deep consultations," Khan said.
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.
Earlier, a UN diplomat said the objective of the Security Council consultations was to "take the temperature and to inform" the 15 members, and it was not expected to result in any formal position.
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.
A UN statement said Sellstrom's team was "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."