The development of centrifuges is a priority for the agency as it tries to establish how advanced Iran is in developing the technology, which could be used in a weapons programme.
Iran's agreement to answer questions about its nuclear programme is primarily aimed to settle all issues in time for ElBaradei's next Iran report to a meeting of the IAEA's 35-nation board in early March.
"Agreement was reached on the timeline for implementation of all remaining verification issues specified in the work plan. According to the agreed schedule, implementation ... should be completed in the next four weeks," an IAEA statement said.
Mohammed Saeedi, deputy head of Iran's atomic energy agency, said the new deadline was agreed upon at Iranian initiative and would show the world that Tehran's nuclear goals are peaceful.
He said: "Iran has nothing to hide and therefore has no fear to answer remaining questions ... to pave the ground for [the IAEA] to give a transparent report about Iran's programme."
ElBaradei met Iranian leaders over two days last week to push for accelerated co-operation to wrap up a long-running IAEA investigation into Iran's current programme, which many suspect is meant to yield an atomic weapon.In Abu Dhabi, the capital of the United Arab Emirates, George Bush, the US president, said on Sunday that Tehran "defies the UN and destabilises the region by refusing to be open and transparent about its nuclear programs and ambitions".
Iran says it wants to refine uranium only for electricity.
After years of diplomatic friction that led to UN sanctions, Iran agreed in August to clarify questions about its nuclear past, a process called the "work plan", within months.
Calling Iran the "world's leading state sponsor of terror", he urged Arab states to join with the US to confront the danger "before it's too late".