UK says informed U.N. chief of more Syria chemical attacks

* New reported attacks in Adra, Daraya and Saraqeb * Syrian government has denied using chemical weapons * U.N. investigative team still unable to enter Syria (Adds diplomat on dates of alleged attacks, Susan Rice, background) By Louis Charbonneau UNITED NATIONS, May 29 (Reuters) - Britain has written to U.N. Secretary-General Ban Ki-moon about additional suspected chemical weapons attacks by Syrian government forces in March and April, British U.N. Ambassador Mark Lyall Grant said on Wednesday. "We continue to inform the Secretary-General and Mr. Sellstrom of any information as, and when, we get it," he said, referring to the Swedish head of a U.N. chemical weapons investigation team, Ake Sellstrom. He declined to provide details, but a U.N. official said on condition of anonymity that the three specific incidents referred to in Lyall Grant's letter have been previously publicized. One was an alleged attack in Adra near Damascus, which a Western diplomat said on condition of anonymity took place on March 24. In that incident, Syrian opposition campaigners said forces loyal to President Bashar al-Assad fired what they said were chemical weapons from multiple rocket launchers at rebel fighters surrounding an army base in the town of Adra on the outskirts of Damascus, killing two fighters and wounding 23. The opposition alleged that Assad's forces used chemical weapons again in late April in Daraya, a suburb of Damascus, and in Saraqeb around the same time. The Western diplomat said the Daraya incident occurred on April 25 and the Saraqeb attack on April 29. The government has denied using chemical weapons and has in turn accused rebels of deploying them in the two-year civil war that the United Nations says has killed over 80,000 people. A senior French official said on Monday that France was testing samples of suspected chemical weapon elements used against Syrian rebels and smuggled out by reporters from Le Monde newspaper and will divulge the results in the next few days. The opposition Syrian National Coalition said in a statement last week that forces loyal to Assad used chemical weapons a second time in Adra in an attack that killed four and injured 50. INCREASING REPORTS OF CHEMICAL ATTACKS Syrian Ambassador Bashar Ja'afari did not respond immediately to a request for comment. A senior U.N. official said last week that the world body was receiving increasing reports of the use of chemical weapons in Syria as the violence escalates. U.S. Ambassador Susan Rice told reporters that U.S. officials have twice briefed Sellstrom and his team "including a few weeks ago in Washington where he had the opportunity to sit with U.S. experts and to hear our best understanding of the information available to us at that time." Sellstrom's team of chemical weapons experts has been ready for more than a month to enter Syria to investigate the allegations but has been held up by diplomatic wrangling and safety concerns. Ban has urged Syria to give the experts unfettered access to investigate all alleged chemical arms incidents. But Assad's government only wants the U.N. team to probe the Aleppo incident from March, not the alleged December Homs attack. U.N. diplomats say U.N.-Syria negotiations on access have reached a deadlock. Britain and France wrote to Ban earlier this year to urge him to investigate three alleged chemical weapons attacks in the vicinity of Homs in December and Damascus and Aleppo in March. Ban has urged Syria to permit Sellstrom's team to investigate both the Homs and Aleppo incidents. Earlier this month, Carla Del Ponte, a member of a U.N. inquiry commission looking at allegations of war crimes in Syria, said the panel had gathered testimony from casualties and medical staff indicating that rebel forces had used the banned nerve agent sarin. But the commission, which is separate from Sellstrom's chemical weapons investigation team, quickly issued a statement distancing itself from Del Ponte's remarks, saying it has reached no conclusions on whether any side in the Syrian war has used chemical weapons. Syria, which is not a member of the anti-chemical weapons convention, is believed to have one of the world's last remaining stockpiles of undeclared chemical arms. (Additional reporting by Mohammed Abbas in London; Editing by Philip Barbara)