Iran is honoring its commitment not to expand atomic activities that could be used to make weapons while it negotiates with six world powers on a lasting nuclear deal, according to a confidential U.N. report released Tuesday.

Obtained by The Associated Press shortly after it was posted on the internal website of the U.N.’s International Atomic Energy Agency, the report could be used by the White House to argue that Iran is negotiating seriously.

The U.S. administration is pushing back against the threat of new sanctions on the Islamic Republic being floated by a bipartisan group of U.S. senators, with President Barack Obama warning that could scuttle the talks. Negotiators seek a framework agreement by March, followed by a comprehensive deal in June putting long-term constraints on Iran’s ability to make nuclear arms in exchange for sanctions relief.

The greatest U.S. concern is Iran’s uranium enrichment program, which can generate grades of material ranging from reactor fuel to the fissile core of nuclear arms.

Iran denies it wants such weapons, but agreed late last year to stop expanding enrichment and other atomic activities while negotiating. The monthly IAEA update said it continued to observe its obligations and was:

— not enriching uranium above 5 percent, which is substantially below the 90-percent level needed for the fissile core of a nuclear weapon.

— diluting or converting most of its stockpile of 20-percent enriched uranium, which can be further enriched to weapons-grade material much more quickly than at 5 percent level.

— not advancing work at an underground uranium enrichment facility thought impervious to last-resort air attacks in an effort to stop Iran’s nuclear program

— maintaining a construction freeze on nearly finished reactor that would produce substantial amounts of plutonium — like highly enriched uranium a source for fissile warhead material.

Diplomats said on Tuesday that the latest negotiating round ending on the weekend in Geneva made some progress, but differences persist over uranium enrichment and other issues.

(AP)