World powers are struggling to reach an interim deal with Iran to limit its nuclear programme, as talks in Geneva move into a second day, BBC News reported.

Iran spoke of "serious issues" that must be resolved, while one Western diplomat cited "considerable gaps". The deal could see Iran curb uranium enrichment for some sanctions relief.

However, U.S. politicians have indicated they will push forward with a bill proposing more sanctions against Iran next month if the talks fail.

U.S. Senate Majority Leader Harry Reid said he would support "broadening the scope" of current oil and trade sanctions.

Both Republican and Democrat congressmen say the threat of sanctions will bolster the negotiating position of the world powers.

President Barack Obama had earlier urged Congress not to promote the bill while talks were going on.

Iran insists its nuclear programme is for peaceful purposes, but some world powers suspect it is seeking a nuclear weapons capability.

The Geneva talks, which are scheduled to conclude on Friday, involve Iran and representatives of the so-called P5+1 - the U.S., UK, France, China and Russia, plus Germany.

Reports suggest the talks could run into the weekend, and U.S. Secretary of State John Kerry may join in later.

EU foreign policy chief Baroness Catherine Ashton is leading the talks for the world powers, and was due to continue meetings with Iranian Foreign Minister Mohammed Javad Zarif on Friday, November 22.