UNITED NATIONS -- The United Nations will investigate accusations that chemical weapons were used earlier this week in Aleppo Province in northern Syria, Secretary General Ban Ki-moon announced on Thursday.
Mr. Ban said the investigation would begin "as soon as practically possible," with various agencies of the world body developing a plan on how to proceed. He called on all sides in Syria's two-year-old civil war to allow "unfettered" access to the United Nations team.
Mr. Ban suggested that the investigation would concentrate solely on a rocket attack on Tuesday that killed 26 people. That attack has become the focus of a propaganda war between supporters of Syria's president, Bashar al-Assad, and his opponents, who accuse each other of firing a missile laden with chemicals in Khan al-Assal, a key eastern area of Aleppo Province.
In a brief statement that he read to reporters, Mr. Ban said he was responding to a formal request made by the Syrian government on Wednesday for a specialized, independent mission to investigate the events in Khan al-Assal. Mr. Ban said he was aware of accusations about a second chemical weapons attack in the Damascus suburbs, but gave no indication that they would be included in the investigation. He did not answer questions from reporters.
Western nations, including the United States, have said in the Security Council that the Aleppo accusations and the Damascus accusations, made by the opposition, should be scrutinized. However, senior American officials have said there is no confirmed indication that chemical weapons were used.
Mr. Ban called the reports of chemical weapons use "disturbing," and said he had sent two letters to Mr. Assad since the conflict began two years ago, reminding him that any chemical weapons stockpiles his country has should be secured.
"I have repeatedly stated that use of chemical weapons by any side under any circumstance would constitute an outrageous crime," Mr. Ban said, adding that anyone who used them "must be held responsible."
Mr. Ban said the inquiry would investigate the reports about Aleppo and "contribute to the safety and security of chemical weapons stockpiles in Syria." He said the Organization for the Prohibition of Chemical Weapons and the World Health Organization would take the lead in organizing the investigation.
Susan E. Rice, the American envoy to the United Nations, issued a statement saying that the United States welcomed the United Nations investigation, stressing that "any and all credible allegations" should be pursued.
The Syrian government should provide unfettered access to "all relevant individuals and locations," it said. Humanitarian workers should be allowed in to treat the injured, the statement also said. It repeated previous American warnings that there would be "consequences" if the Assad government used or failed to secure chemical weapons.
The chemical weapons claims on Wednesday were immediately entangled in the longstanding sharp divisions between Russia, Syria's most powerful remaining ally, and Western states that oppose the Damascus government. The accusations and demands for an outside investigation ignited a tense discussion in the Security Council about how to respond.
The Syrian ambassador to the United Nations, Bashar Jaafari, told reporters that his government had requested an official inquiry to corroborate its claims that insurgents, not government forces, were behind the attack. Mr. Jaafari said he had delivered a letter to Mr. Ban's office seeking a "specialized, independent and neutral technical mission" to investigate the use of chemical weapons by the opposition.
The opposition has denied possessing or using chemical weapons. In the Security Council debate, France said the United Nations should investigate the opposition's accusations against the government, in Aleppo Province and in the Damascus suburbs. Russia responded by accusing the West of trying to create a diversion.
The Russian envoy, Vitaly I. Churkin, said the United States, France and others were engaged in "delaying tactics." "Instead of launching those propaganda balloons, it is better to get our focus right," said Mr. Churkin, adding that the Western demands echoed the demands more than a decade ago for inspections in Iraq, which failed to find any chemical weapons.
Mr. Churkin and Mr. Jaafari each suggested that the opposition faked a chemical attack by the government to provoke international intervention. The Syrian ambassador said it would not be surprising for the opposition to try to manufacture a crisis while President Obama was visiting the region.
The French envoy, Gerard Araud, sarcastically referring to Mr. Churkin's summary of the council debate as "fascinating," said France and its allies wanted the United Nations to investigate all possible incidents. "It is not a question of delay; it is a question of looking at all the allegations which have been tabled," Mr. Araud said.
That position was echoed by Britain and the United States. "The facts are not clear at the moment, and this is the whole point," said Philip Parham, Britain's deputy permanent representative.
France and Britain sent their own letter to Mr. Ban later Thursday demanding that all chemical weapons accusations emerging from Syria be thoroughly documented, including the latest two and one from Homs in December. The United Nations can claim a mandate to investigate matters beyond those requested by the Syrian government, Security Council diplomats said.
This article originally appeared in The New York Times.