WASHINGTON  - The United States unleashed a fresh wave of sanctions against Iran Thursday, ratcheting up pressure to convince Tehran to take seriously concerns about its suspected nuclear weapons program.The actions impose additional sanctions on Iran’s “nuclear and ballistic missile proliferation networks” and identifies more than 50 Iranian “front companies and banks,” the Treasury Department said. “These actions are part of the United States government’s dual-track approach of increasing pressure to convince Iran to engage seriously and address the international community’s concerns about its nuclear program. David Cohen, the Treasury’s under secretary for terrorism and financial intelligence, said the moves take “direct aim at disrupting Iran’s nuclear and ballistic missile programs as well as its deceptive efforts to use front companies to sell and move its oil. We will continue to ratchet up the pressure.” The United States and European Union have implemented an oil embargo against Iran, leading to a substantial decline in exports of crude from which the Islamic republic draws two-thirds of its foreign exchange earnings. Iran been subject to severe international economic sanctions over its controversial nuclear program, which Western powers believe masks an atomic weapons drive despite repeated denials by Tehran.  In Thursday’s actions, the US Treasury and State departments targeted 11 entities and four people, alleging that many of them are part of a network of proliferators headed by Iran’s Ministry of Defense for Armed Forces Logistics and its subsidiary, Aerospace Industries Organization.A number of sanctions were added against Iran’s national maritime carrier, Islamic Republic of Iran Shipping Lines, and Iran’s Islamic Revolutionary Guard Corps.Both the IRISL and the IRGC has been the target of a numerous sanctions actions by the United States and its partners, the department noted.On Thursday, US Secretary of State Hillary Clinton urged Southeast Asian nations to help keep up pressure on Iran and end a diplomatic stalemate over talks on its suspect nuclear program. The United States viewed regional body ASEAN “as a partner in the broad international effort to prevent Iran from acquiring nuclear weapons,” Clinton told a meeting of East Asian nations in Cambodia, according to the text of a speech released to the media.“The best way to achieve the diplomatic solution we all seek is for the international community to stay united and to keep up the pressure that has brought Iran back to the negotiating table,” she said.World powers have been pushing Tehran to abandon its enrichment of uranium, accusing the Islamic republic of trying to develop a nuclear weapon. Iran denies the accusations saying its nuclear programme is for civilian use only.So far, Iran and the P5+1 group of powers - the five permanent UN Security Council members plus Germany - have failed to reconcile their views on the nuclear issue.“If we ease the pressure or waver in our resolve, Iran will have less incentive to negotiate in good faith or to take the necessary steps to address the international community’s concerns about its nuclear programme,” Clinton warned.Numerous countries initially voiced concern about the US law. China and India were among the most outspoken, protesting that their energy-hungry economies should not be beholden to US domestic law.Just days before it came into force Washington exempted China and Singapore from sanctions over purchases of oil from Iran, saying major economies were united in pressuring Tehran.But the United States did not grant exemptions to smaller-scale importers such as Pakistan, meaning that its banks could face punishment if they handle transactions for Iranian oil.