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.
In addition, the Treasury identified four entities - Petro Suisse Intertrade, Hong Kong Intertrade, Noor Energy and Petro Energy Intertrade - as front companies used to enable evade sanctions on its oil exports.
All four were accused of being fronts for Iran's National Oil Company.
The US also identified 58 vessels of the National Iranian Tanker Company as owned by the Iranian government, in a move aimed at preventing Iran from circumventing oil sanctions by concealing its tankers.
The US and the European Union already have a wide range of sanctions in place aimed at putting pressure on Iran to make concessions on its nuclear programme.
Many of the steps are aimed at preventing Iran from selling its oil on the international market.
They include a US measure banning banks around the world from completing oil transactions with Iranian banks, as well as several sanctions targeting Iran's central banks.
In addition, the EU banned all imports of Iranian crude oil in July.
The latest round of talks between six world powers and Iran on Tehran nuclear programme, held in Moscow, ended without a breakthrough.
The so-called "P5+1" group - the permanent members of the UN Security Council and Germany - want Tehran to suspend the enrichment of uranium to a level of 20%, close down an underground enrichment facility near the city of Qom and export its stockpile of 20%-enriched uranium.
In return, the six said they were prepared to offer help with nuclear safety measures.
Iran demanded that the West lift its sanctions, including the EU oil embargo and the US measures against its central bank, as well as recognise its "non-negotiable" right to enrich uranium.
The two sides agreed to downgrade negotiations to a technical level before deciding on whether to hold further high-level talks.