Russia calls on Syria, rebels to allow probe of alleged attack The government of Syrian President Bashar al-Assad has strenuously denied launching a chemical attack. But opposition forces who have waged a bloody civil conflict against the government for 2 1/2 years say they believe Syrian forces used fatal poison gas on civilians, including women and children. U.N. Secretary General Ban Ki-moon sent his top disarmament official to Damascus on Thursday to secure permission for international weapons investigators already in the country to examine the alleged site and interview witnesses. "I can think of no good reason why any party, either government or opposition forces, would decline this opportunity to get to the truth of the matter," Ban told a diplomatic forum in Seoul on Friday, according to comments carried by Reuters news agency. But activists inside Syria say they hold out little hope that the U.N. team - which arrived in Syria after months of negotiates, to investigate earlier, smaller attacks - will be allowed into the eastern suburbs of Damascus where the more recent attack allegedly took place. As a result, activists said, they are working to smuggle skin, hair and blood samples to inspectors in an effort to prove their claims. On Wednesday, an effort by members of the U.N. Security Council to demand an investigation was stymied, in part, by Russian resistance. But Russia's Foreign Ministry said Friday that Foreign Minister Sergei Lavrov and U.S. Secretary of State John F. Kerry spoke by phone Thursday and agreed that it is a matter of "general interest" to conduct an impartial investigation into the allegations. "Immediately upon receipt of relevant information, the Russian side called on the government of Syria to cooperate with the U.N. chemical experts," the Foreign Ministry statement said. The task now for the opposition is to provide secure access to the proposed site of the incident. The statement also said Russia is seeking "constructive progress from the opposition in regard to the early convening of an international conference on the political settlement of the Syrian crisis." In an interview that aired Friday morning on CNN, Obama called the reports of an attack "very troublesome" and said he faces an abbreviated timetable to decide how to respond. Gruesome photos, videos and witness accounts that have circulated so far, Obama said, indicate that "this is clearly a big event of grave concern." Obama said the use of chemical weapons "starts getting to some core national interests that the United States has, both in terms of us making sure that weapons of mass destruction are not proliferating, as well as needing to protect our allies, our bases in the region. . . . This is something that is going to require America's attention. Asked about the possibility of U.S. intervention, however, Obama told CNN anchor Chris Cuomo that he had to weigh carefully what he thinks is in the best short- and long-term interests of the United States. "We remain the one indispensable nation," said Obama, who was interviewed in the midst of his college campus bus tour in New York and Pennsylvania. There's a reason why, when you listen to what's happened around Egypt and Syria, that everybody asks what the U.S. is doing. It's because the United States continues to be the one country that people expect can do more than just simply protect [its] borders. At the same time, Obama said,"that does not mean that we have to get involved with everything immediately," despite calls for action from opposition groups and some U.S. lawmakers. "We have to think through strategically what's going to be in our long-term national interests, even as we work cooperatively internationally to do everything we can to put pressure on those who would kill innocent civilians," Obama said. "Jumping into stuff that does not turn out well," the president added, "gets us mired in very difficult situations, [and] can result in us being drawn into very expensive, difficult, costly interventions that actually breed more resentment in the region." Alexia Jade, an activist with the opposition group Damascus Media who uses a pseudonym, said human blood, hair and skin samples had been collected from victims of the alleged attack, in addition to samples from dead animals. She described the task of getting the samples to the U.N. team as a "very complicated mission," saying the weapons inspectors were surrounded by government minders. Rucker reported from New Milford, Pa. Will Englund contributed to this report from Moscow.