Damascus (CNN) -- United Secretary General Ban Ki Moon said Friday that allegations the Syrian regime used chemical weapons should be investigated immediately, saying such a "crime against humanity should result in serious consequences for the perpetrator." Ban, speaking in South Korea, said he had called on the Syrian government to allow a U.N. inspection team currently in Syria to examine previous claims of chemical weapons use swiftly to access the site of the latest alleged attack. He is also sending the U.N. High Representative for Disarmament Affairs, Angela Kane, to Damascus to press the case for an urgent investigation. "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 said. The images of victims from this incident, including many children, are "heartbreaking and sickening," Ban said. "Any use of chemical weapons anywhere, by anybody, under any circumstances, would violate international law. Such a crime against humanity should result in serious consequences for the perpetrator." Anti-regime activist groups in Syria say more than 1,300 people were killed in the attack Wednesday in Ghouta, outside Damascus -- many of them women and children. Graphic video footage showed rows of bodies without apparent injury, as well as people suffering convulsions or apparently struggling to breath. CNN could not immediately verify where or when the videos were recorded, and could not authenticate the number killed or injured. Ban said the situation in Syria, where rebels have been fighting the forces of President Bashar al-Assad for more than two years, continues to worsen. The death toll has now surged past 100,000, he said. A million child refugees Meanwhile, two U.N. agencies said Friday that the number of child refugees from Syria has now passed a landmark threshold, with 1 million forced to flee during the conflict. They make up half of all refugees from the country. About 740,000 of the children registered are aged under 11, U.N. children's agency UNICEF said. Most have arrived in Lebanon, Jordan, Turkey, Iraq and Egypt, with some families also heading to North Africa and Europe. "This one millionth child refugee is not just another number," said UNICEF Executive Director Anthony Lake. "This is a real child ripped from home, maybe even from a family, facing horrors we can only begin to comprehend." Inside Syria, some 7,000 children have been killed during the conflict, according to the Office of the High Commissioner for Human Rights, while another 2 million children have been internally displaced. The apparent presence of many small children among the victims of Wednesday's alleged attack will add to concerns for the safety of Syria's most vulnerable citizens. Claims denied Al-Assad's government has denied any claims it used chemical weapons. "Everything that has been said is absurd, primitive, illogical and fabricated," said Syrian Information Minister Omran Zoabi on state TV. He said the claim was timed by the opposition to coincide with the U.N team's visit and came as government forces were making gains on all sides against the rebels. In the streets of government-controlled Damascus, many people said they do not believe the government resorted to the use of nerve agents. "The government would never use chemical weapons because Bashar al-Assad is part of the country, he grew up here, they are Syrians," one man told CNN. Another said he believed that if anyone was hit, it was members of the rebel Free Syrian Army. Residents confirmed that there appeared to be a massive military operation under way early Wednesday, with war planes dropping bombs and artillery firing for hours. Staff at the Mezzeh University hospital told CNN they received many casualties on Wednesday from the area allegedly hit by the attack. But, they said, the casualties showed no signs of having been subjected to chemical agents. However, experts who have viewed footage purportedly from the scene say it indicates that some form of chemicals seem to have been used. Red lines The allegations have prompted a wave of international condemnation and spurred calls Thursday for the United Nations to act. Turkey's foreign minister, Ahmet Davutoglu, said Thursday that "all red lines" have been crossed in Syria and that the United Nations cannot be indecisive about chemical weapons attacks there. His French counterpart, Laurent Fabius, said force must be used if the claims of chemical weapons use were proven, although he ruled out the use of ground troops. President Barack Obama has directed the U.S. intelligence community to urgently gather additional information to try to assess whether chemical weapons were used Wednesday, State Department spokeswoman Jen Psaki said Thursday. At this time, she said, the United States is unable to "conclusively determine" chemical weapons use, but is focused on trying to nail down the facts, along with its international partners. Psaki said, as she has before, that if reports of chemical weapons use prove true, the president has a range of options available to him to respond. Later, a senior defense official told CNN that "the military continues to refine options for Syria to be prepared for whatever the president might request down the line." International law U.N. High Commissioner for Human Rights Navi Pillay said the matter is "of utmost urgency" and the "allegations are exceptionally grave." Pillay urged both the government and opposition to enable investigators "to examine the site of the alleged attacks without any delay or obfuscation." "The use of chemical weapons is prohibited under customary international law," she said, noting that the prohibition is binding on the government and rebels. "Whether or not chemical weapons were in fact used, it seems that once again in Syria many civilians have been killed in flagrant contravention of international law." U.N. special advisers Adama Dieng and Jennifer Welsh similarly urged immediate access for the U.N. investigation. "There is never any military justification for the use of chemical weapons -- whether by governments or anti-government armed groups -- given their horrific and indiscriminate impact," they said in a joint statement.