BEIRUT–Syria’s deputy oil minister announced his defection in an online video that emerged Thursday, making him the highest ranking official to abandon President Bashar Assad’s regime since the country’s uprising erupted a year ago. The defection of Abdo Husameddine, who said he was joining the opposition because of the “brutal” crackdown on dissent that has claimed the lives of thousands of Syrians, came as the U.N.’s humanitarian chief Valerie Amos said she was “struck” by the devastation she saw in a shattered district of the central city of Homs. Amos is the first independent outside observer to be allowed in Hom’s Baba Amr since the military overran the district, wrestling it from rebel control on March 1 following a monthlong assault that brought international condemnation. She was allowed a brief tour in the ravaged district on Wednesday. “The devastation there is significant. That part of Homs is completely destroyed and I am concerned to learn what happened to the people in that part of the city,” she said in Damascus, after meeting with Syria’s education and health ministers on Thursday. In Cairo, former U.N. chief Kofi Annan said his top priority as special envoy to Syria is to end the violence and deliver badly needed aid. Annan, who has been appointed joint U.N.-Arab League envoy to Syria, said his mission was to start a “political process” in Syria to resolve the one-year conflict there. Addressing a news conference after talks on Thursday with Arab League chief Nabil Elaraby in Cairo, Annan said he has the full backing of the international community for his mission. He is scheduled to travel to Damascus on Saturday, where he will likely meet Assad. Assad’s power structure has seen a steady stream of army defectors who have joined a group of dissidents known as the Free Syrian Army, now numbering in the thousands, but civilian government officials have remained largely loyal. “I do not want to end my life servicing the crimes of this regime,” Husameddine said, announcing his resignation in a video on YouTube. He identified himself as an “assistant” to the oil minister and a member of the ruling Baath Party and said he has served 33 years in various government positions. Ministers in Syria may have several assistants known as deputies. In the video, Husameddine is shown wearing a suit and tie and sitting on a sofa at an undisclosed location, reading from a paper. “I, Abdo Husameddine, deputy oil and mineral resources minister, announce my defection from the regime and resignation from my post … and declare that I am joining the dignified people’s revolution,” he said.