(Reuters) - The timing and scope of sanctions relief are among crucial sticking points as Iran and the six major world powers resume talks in Vienna on Wednesday to discuss a nuclear agreement aimed at curbing Tehran's nuclear activities by June 30.

The exact timing of the start of the talks has not been made public.

After a tentative deal between Iran and the six powers was reached in Switzerland on April 2, different interpretations emerged over what was agreed in the framework, suggesting that nailing down a final agreement will be tough.

"Lifting sanctions will be one of the main topics in this round of talks … If the other party shows political good will, we can reach a final agreement," Iran's deputy foreign minister Abbas Araqchi told Iranian state TV on Wednesday.

Iran insists it would only accept a final deal over its contested nuclear program if world powers simultaneously lifted all sanctions imposed on it.

The United States has made it clear that sanctions on Iran would have to be phased out gradually under the final pact.

Iran and the powers are trying to end more than 12 years of diplomatic wrangling over the country's disputed nuclear program, which Tehran says is peaceful but Western powers fear is aimed at developing an atomic bomb.

U.S. President Barack Obama was forced to give Congress a say in any future accord - including the right of lawmakers to veto the lifting of sanctions imposed by the United States.

Araqchi said on state television on Wednesday that the U.S. administration was "responsible to ensure that its commitments, particularly sanctions-related ones, are fulfilled".

Many other issues also must be hammered out before the end-of-June deadline for the final accord.

European Union political director Helga Schmid is set to meet Araqchi on Wednesday, followed by talks between Iran and political directors from the six powers.

By Reuters