Delhi Chief Minister Arvind Kejriwal said on Saturday he felt sapped by the day-to-day "interference" by the central government and this was the main reason why he was not holding any portfolio himself as all this had forced him to function like a "foreign relations" minister."The day-to-day interference has sapped us badly. It is the biggest challenge," he said referring to the bitter feud between the Delhi and central governments.He said any good decision taken by his government was declared "null and void" by Lt. Governor Najeeb Jung. "The Lt. Governor has been like a headmaster...," Kejrwal said, lamenting: "You need the space to govern.""I handle the politics of this Delhi governance and all the ministers-handled governance. One is politics and second is.... I would call it external relations."Jung, who reports to the Centre, had been accused by the Aam Aadmi Party government of hindering its work.