BEIRUT - Damascus should allow greater humanitarian access to people in need inside Syria, the United Nations' aid chief said on Monday after his first visit to the country.Stephen O'Brien, who took up his post in May, also condemned Syrian air strikes that killed nearly 100 people outside the capital during his visit, saying actions by all sides fighting in the four-year conflict were "unacceptable"."The dire catastrophe, which is the humanitarian situation in Syria... is worsening," he told Reuters in Beirut after weekend meetings with Syria's foreign minister and deputy foreign minister."It was therefore very much central to the discussions I had with government ministers that we need to have that unimpeded access... (to) all people who are vulnerable and in need," he said.O'Brien visited Damascus and the central Syrian city of Homs. He condemned Syrian army air strikes on the city of Douma, northeast of Damascus, which were reported to have killed almost 100 people, after his meetings with officials"As I was having discussions - it became apparent shortly afterwards - that there had been these air strikes. Like others, I was horrified... it is absolutely vital to recognize that that is unacceptable."Equally, I saw the effects of yet more cuts to the water supply in parts of Damascus from those who are on the other side of the argument. It is clear to me that those cutting water supplies as a weapon of war, it is unacceptable," O'Brien said.The Syrian civil war has killed an estimated quarter of a million people and driven more than 11 million from their homes.