By PETER JAMES SPIELMANN Bashar Ja’afari, Syria’s U.N. ambassador, gestures as he speaks during a news conference, Tuesday, April 30, 2013 at United Nations headquarters. Bashar Ja’afari says the use of chemical weapons is not only “a red line” but “a blood line” that cannot be tolerated and is again demanding a U.N. investigation of an alleged chemical weapons attack in Aleppo that it blames on rebels. (AP Photo/Mary Altaffer) UNITED NATIONS (AP) — Syria’s U.N. ambassador said Tuesday that the use of chemical weapons is not only “a red line” but “a blood line” that cannot be tolerated and again demanded a U.N. investigation of an alleged chemical weapons attack in Aleppo that it blames on rebels. Bashar Ja’afari said at a news conference that his government has bodies and other proof that chemical weapons were used in Khan al-Assad in Aleppo on March 19 and it wants this incident investigated first. The rebels blame the government for the attack. Ja’afari said Damascus is demanding details of another alleged chemical weapons attack that Britain and France say was carried out by the government in Homs on Dec. 23 before it will even consider allowing U.N. experts to conduct an investigation in that city. He disclosed that Qatar also sent a letter to the United Nations “claiming the use of chemical weapons in other parts of Syria,” without giving dates or locations. Pressed by reporters, Ja’afari declined to confirm that Syria has chemical weapons. “The Syrian government has always emphasized that the Syrian government will not use, if it possesses any, chemical weapons on its own people,” he said. He added, “The use of chemical weapons in Syria and elsewhere in the world is not only a red line, it’s a purple line, it’s a blood line, and nobody is tolerated or will be tolerated to use such horrific weapon of mass destruction.” He was speaking as President Barack Obama strongly suggested at a news conference in Washington that he would consider military action against Syria if it can be confirmed that President Bashar Assad’s government used chemical weapons in the country’s two-year-old civil war, which the U.N. says has killed more than 70,000 people. Obama said that while there is evidence that chemical weapons were used inside Syria, “we don’t know when they were used, how they were used. We don’t know who used them. We don’t have a chain of custody,” he said. If it can be established that the Syrian government used chemical weapons, he added, “we would have to rethink the range of options that are available to us.” Ja’afari blamed opponents of the Syrian government, which he didn’t name, for launching “a campaign of incitement” which has included “trumped-up charges and fraudulent accusations against Syria” as well as a media, diplomatic and political campaign. He said it was similar to the campaign leading to the Iraq War in 2003, when the United States and Britain claimed Iraq had weapons of mass destruction. The claim proved to be false. “What happened in Iraq is still alive in our minds,” he added. Ja’afari insisted that the U.N. team of chemical weapons experts should immediately go to Syria to investigate the Khan al-Assad incident, but made no commitment to investigating the other claims. “The Syrian government is still waiting to receive information on these situations,” Ja’afari said. “Then, if the Syrian government and the secretary-general and the Security Council members feel that these allegations are also credible, the Syrian government might — might — examine the possibility of asking for further investigation,” he said. If such information is delivered to Damascus, “then it would be up to us” to make a decision, Ja’afari said. U.N. spokesman Martin Nesirky said later that the U.N. experts “will look into the incidents in the order received,” so the Khan al-Assad attack “is the first one, but the secretary-general feels that he cannot engage in a partial investigation, there needs to be investigation of all allegations.” Nesirky approved of Syria’s desire to have a quick investigation of Khan al-Assad. “However, such cooperation should also be extended to Homs, the site of the other allegation,” he said. ___ Associated Press Writer Edith M. Lederer contributed to this report from the United Nations.