WASHINGTON (AFP) - The US kept up pressure on Iran Tuesday with fresh sanctions on two groups accused of illicitly aiding the country even as negotiations continue over Tehran's nuclear programme.

The US Treasury set sanctions on a Chinese group accused of supporting Iran's ballistic missile program and a Dubai group which allegedly helps Iran evade restrictions in exporting its oil.

Eight China-based companies linked to already-sanctioned businessman Karl Lee, or Li Fangwei, were blacklisted. The Treasury said Lee had used them as front companies to export materials to Iran for its ballistic missile programme.

The Treasury also named Dubai businessman Saeed al-Aqili, his Al Aqili Group LLC, and a Dubai-based Pakistani "financial facilitator", Anwar Kamal Nizami, for helping Iran avoid international sanctions on its oil exports.

The Treasury's move to blacklist both groups forbids US citizens or businesses from transactions with them and freezes any assets they may have in a US jurisdiction.

The new sanctions come even as Washington, as part of the "P5+1" powers in negotiations with Tehran, have loosened general sanctions on the country's economy as an incentive to make progress on halting what is believed is Iran's effort to develop nuclear weapons.

After a temporary deal on the issue was struck in November, the group - the US, Britain, France, China and Russia plus Germany - is now seeking a permanent accord against a July 20 deadline.

"As we have made clear, we will continue vigorously to enforce our sanctions, even as we explore the possibility of a comprehensive deal addressing Iran's nuclear programme," said Treasury Under Secretary for Terrorism and Financial Intelligence David Cohen in a statement.