Britain, France claim Syria used chemical weapons UNITED NATIONS - Britain and France have informed the United Nations that there is credible evidence that Syria has used chemical weapons on more than one occasion since December, according to senior diplomats and officials briefed on the accounts. In letters to U.N. Secretary General Ban Ki-moon, the two European powers said soil samples, witness interviews and opposition sources support charges that nerve agents were used in and around the cities of Aleppo, Homs and possibly Damascus, said the officials, who spoke on the condition of anonymity because of the sensitivity of the matter. Interactive Grid: Keeping track of the conflict in Syria through videos, images and tweets. Latest stories on Syria Colum Lynch and Karen DeYoung Assad government insists rebels were behind attack in Aleppo; U.S. still investigating allegations. Karen DeYoung Defense Secretary Hagel says administration remains opposed to military aid to Syrian rebels. 40 years after cease-fire, Israelis in the Golan Heights watch as Syria's civil war edges ever closer. Many in the opposition say the Brotherhood uses its support and money as key levers for influence. Liz Sly U.S. aid to Syrians in rebel-held areas is kept quiet to protect aid workers and recipients. Ryan Lucas Three children were among those killed in the attack on a town in the country's northwest. Bassem Mroue The regime offensive comes after the rebels, resupplied with arms, have been advancing steadily. The European reports are in part aimed at countering accusations by the Syrian government that opposition forces had used chemical weapons during fighting in the town of Khan al-Asal near Aleppo on March 19, killing 26 people, including regime troops. Syrian rebels have said that government forces used chemical weapons in the incident. James R. Clapper Jr., the director of national intelligence, told a Senate panel Thursday that allegations that the Syrian government had used chemical weapons are still being evaluated. A U.S. conclusion that the evidence is valid would increase pressure on President Obama to step up assistance to the Syrian opposition. Obama has called any use of chemical weapons in Syria a "game changer." The administration has resisted providing even significant nonlethal aid to rebel fighters because it remains unconvinced that the supplies would not end up with extremists linked to al-Qaeda. At the same time, it has grown increasingly frustrated at the disunity of the Syrian political opposition it is counting on to freeze out the extremists. That frustration is shared by the core group of governments most involved in the effort to oust Syrian President Bashar al-Assad - including the United States, Britain, France and countries in the region - which are divided on what to do about the rapidly worsening crisis. The British and French chemical weapons claims may add a new dimension to Obama administration deliberations. After the Aleppo incident, Assad officials countered that the rebels, not the government, had used chemical weapons, The regime called for a U.N. investigation. The U.N. chief appointed a team of investigators, but they have not been allowed inside Syria. Key Western powers have demanded that the team investigate all reported incidents. Syria, backed by Russia, has said that the investigators would be restricted to the Aleppo site. In an April 6 letter to Ban, Syrian Foreign Minister Walid al-Moualem suggested that his government might be willing to accept a more expansive investigation, but only under certain conditions. European diplomats acknowledged that Syrian forces may have been exposed to chemical agents during the Aleppo attack, but they said it was a "friendly fire" incident in which the troops were hit when a government shell missed its opposition target. The diplomats cautioned that they suspect the Syrian government has used the weapons only in rare cases and said they believe it was testing the response of the United States and other Western powers.