European Union governments have imposed sanctions against major Iranian state companies in the oil and gas industry, and strengthened restrictions on the central bank, cranking up financial pressure over Tehran's nuclear programme.
More than 30 firms and institutions were listed in the EU's Official Journal as targets for asset freezes in the EU, including the National Iranian Oil Company (NIOC), a large crude exporter, and the National Iranian Tanker Company (NITC).
Both are vital to the Iranian oil industry, the main source of revenue for the government.
Their importance has risen in recent months as the European Union and the United States seek to reduce Tehran's access to cash by forcing Western companies to halt trade with Iran.
Iran said the sanctions would not work.
"We recommend that, instead of taking the wrong approach and being stubborn and using pressure, ... with a logical approach they can return to discussions," foreign ministry spokesman Ramin Mehmanparast told a news conference.
FRESH IRAN TALKS EYED
The new listings follow a decision on Monday by the 27 EU governments to bring sweeping new sanctions against Iranian banking and energy sectors to try to draw Tehran into serious negotiations about its atom project.
A spokesman for EU foreign policy chief Catherine Ashton said six powers negotiating with Iran were hoping to resume talks soon but that no more meetings had yet been scheduled.
"We focus our sanctions on those who are responsible for the (Iranian) nuclear programme, while at the same being open to talks," Michael Mann told a regular news briefing in Brussels.
"We have always said we don't do sanctions for their own sake."
Iran denies its work has any military intentions and says it will not scale back activities unless sanctions are lifted.
But Europe and the United States are increasing sanctions pressure amid fears of an Israeli attack on Tehran's nuclear facilities, which could lead to a new war in the Middle East.
In Tuesday's list, the European Union also targeted NIOC subsidiaries, as well as the National Iranian Gas Company and National Iranian Oil Refining and Distribution. Several banks were also listed.
MALTA'S POSITION
The Maltese Foreign Ministry said Malta has consistently supported the EU's dual track approach with Iran.
"Whilst being part of the consensus on restrictive measures, Malta, like its fellow EU Member States would much prefer a diplomatic solution and would welcome a serious engagement by Iran that is genuinely aimed at addressing the valid concerns of the international community regarding the aims of its nuclear programme."
Malta is legally obliged and politically committed to implementing all sanctions that the United Nations and European Union have put in place regarding Iran.
However the new sanctions are not expected to have any impact on the Maltese economy. Malta Freeport was impacted in the first round of EU sanctions when the EU imposed sanctions against Iranian shipping companies.