WASHINGTON: Economic sanctions in place for decades have not stopped Iran from pursuing nuclear ambitions or, if administration allegations are true, from funding terror across the Middle East.

So why would the sanctions announced on Thursday – a big dose of more of the same – cause Iran to change its policies?

The latest sanctions might even make Iran dig in more, analysts said.

“It is unlikely to directly affect Iranian behaviour on the nuclear side,” said Robert Hunter, a Middle East expert and senior adviser at the Rand Corp.

“It is a symbolic message to Iran and everyone else that the US is deadly serious.”

The United States has had only mixed results using sanctions as a foreign policy tool in the past against countries like Iran, Cuba and North Korea.

Under decades-old US financial sanctions, virtually all trade and investment activities with the government of Iran, including government-owned banks, are prohibited.

Other sanctions, such as those imposed on Thursday, have hit Iranian entities that the United States believes are linked to terror activities and the proliferation of weapons of mass destruction.

Despite all that, the United States says Iran funnels hundreds of millions of dollars a year to Hezbollah, Hamas and other groups the United States consider terror organisations. The United States has called the country a “central banker of terror.”

Teheran also has not backed down from its nuclear ambitions, which the Bush administration insists are to make nuclear weapons.

Iran’s defiance of UN Security Council demands that it stops uranium enrichment has led to two sets of economic sanctions. A third, tougher set of UN sanctions has been stalled by opposition from China and Russia.

The United States and some of its allies accuse Iran of secretly trying to develop nuclear weapons and have demanded it halts uranium enrichment, a step both to the production of energy and the production of atomic weapons. Iran denies the claim, saying its program is for peaceful purposes only, including generating electricity.

Secretary of State Condoleezza Rice, in announcing the new sanctions with Treasury Secretary Henry Paulson, said Washington remains open to a “diplomatic solution.”

The latest sanctions against Iran, the harshest since the takeover of the US Embassy in 1979, include among other things targeting Iran’s Revolutionary Guard Corps, part of the country’s military, as well as the Iran’s special operations unit, Quds Force, which is part of the Guard Corps.

Three of Iran’s largest banks – Bank Melli, Bank Mellat and Bank Saderat – also were targeted. The United States had already moved in 2006 to sever Bank Saderat from the US financial system.

The order also designates companies, including Khatam al-Anbya Construction Co. and Oriental Oil Kish, believed to be owned or controlled by the Revolutionary Guard Corps, as well as military officials and people involved in Iran’s ballistic missile programs.

Under the action, any financial assets found in the United States belonging to those named on Thursday must be frozen. Americans also are prohibited from doing business with them. Essentially those targeted are frozen out of the United States, the world’s largest economy and home to the globe’s most influential banking system.

Importantly, the new sanctions can make others outside the United States think twice about having relationships with those blacklisted. That requires skilful financial diplomacy.

The United States, which has been pressing allies in Europe, Japan and elsewhere, has had only limited success with persuading financial institutions outside this country voluntarily to sever or scale back business with Iran.

It is a challenge given Iran’s standing in the global economy and its position as a major oil supplier. That makes Iran an attractive investment for companies.

For the new US sanctions to be truly effective, the United States needs to persuade other countries to follow suit.

“So far, however, the administration has presented only the broad outline of a justification for its actions, not the comprehensive details required to be convincing,” said Anthony Cordesman of the Centre for International and Strategic Studies.

“There has been no mention of how they relate to US efforts to work with Britain, France and Germany or in the context of the UN,” he said.

“There may well be a good, practical case for the new sanctions, but so far, the administration is acting as if there was no world beyond the Beltway,” he said, referring to the highway that encircles Washington.