Iran - The United States says it has further tightened sanctions on Iran imposed in connection with its nuclear programme.

The US Treasury said it had blacklisted several companies and individuals that it believes are contributing to efforts to acquire nuclear weapons.

It also said it had identified several companies and banks acting as front organisations helping Iran to evade existing sanctions.

  Iran insists its nuclear programme is purely for peaceful purposes.

"We will continue to ratchet up the pressure so long as Iran refuses to address the international community's well-founded concerns about its nuclear programme," US Treasury official David Cohen said.

He added that the latest steps were aimed at "disrupting Iran's nuclear and ballistic missile programmes, as well as its deceptive efforts to use front companies to sell and move its oil".

The blacklisting measures target 11 companies involved in Iran's nuclear and ballistic missiles programmes, and with links to the defence ministry, the Revolutionary Guards and the national shipping line, the rUS Treasury statement said.

They also covered four individuals said to be supporting Iran's nuclear programme, among them the commander of the Revolutionary Guards' navy, Ali Fadavi.