Iranian foreign minister returns to nuclear talks in Vienna amid signs of backtracking

U.S. Secretary of State John Kerry, left, meets with Russian Foreign Minister Sergey Lavrov at a hotel in Vienna Tuesday June 30, 2015. Talks continued in Vienna Tuesday on Iran's nuclear programme. (Carlos Barria/Pool, via AP) (The Associated Press)

U.S. Secretary of State John Kerry, smiles during his meeting with Russian Foreign Minister Sergey Lavrov at a hotel in Vienna Tuesday June 30, 2015. Talks continued in Vienna Tuesday on Iran's nuclear programme. (Carlos Barria/Pool, via AP) (The Associated Press)

Iranian Foreign Minister Javad Zarif laughs during a meeting with U.S. Secretary of State John Kerry at a hotel in Vienna, Austria, Tuesday June 30, 2015. Pushing past a deadline, world powers and Iran extended negotiations for a comprehensive nuclear agreement by a week on Tuesday as the U.N. nuclear agency prepared to announce Tehran had met a key condition. (Carlos Barria/Pool via AP) (The Associated Press)

Iran's foreign minister has returned to the nuclear talks in Vienna where negotiators are struggling to overcome still significant differences and preparing to work through a self-imposed deadline for a deal.

Iranian Foreign Minister Mohammad Javad Zarif was rejoining the talks Tuesday after consultations in Tehran and was to meet U.S. Secretary of State John Kerry. Zarif arrived in Vienna with Ali Akbar Salehi, the head of Iran's atomic agency, who had missed earlier sessions due to illness. Iran's official news agency said Salehi's participation indicated Iran's serious desire to accelerate the talks and achieve a comprehensive deal. Russian Foreign Minister Sergey Lavrov was also expected to join the discussions.

On Monday, U.S. officials suggested that significant backtracking by Tehran's negotiators may need several more days of discussions to resolve.