Strategic Affairs Minister Yuval Steinitz said Iran still believed it had room for maneuver in dealing with world powers, and that unless it faced a credible threat of U.S. military action, it would not stop its nuclear activities.
"There is no more time to hold negotiations," Steinitz, who is close to Prime Minister Benjamin Netanyahu, said in an interview with the Israel Hayom daily published on Friday.
The United States and its allies suspect Iran is working towards a nuclear weapons capability despite Tehran's insistence that its atomic program has only peaceful aims.
During four years of international negotiations over its disputed nuclear program, during which U.N.-sponsored sanctions have hit Iran's economy hard, Steinitz said the Islamic Republic had only improved its capabilities.
"If the Iranians continue to run, in another half a year they will have bomb capability," he said.
Israel has dismissed overtures to the West by new Iranian President Hassan Rouhani, and his pledge in an interview on U.S. television that Iran would never develop nuclear weapons.
"One must not be fooled by the Iranian president's fraudulent words," Netanyahu's office said in a statement on Thursday. "The Iranians are spinning in the media so that the centrifuges can keep on spinning."
Both Israel and the United States have hinted at possible military action to prevent a nuclear-armed Iran should sanctions and diplomacy fail to curb its atomic program.
But Steinitz said a phrase used often in the past by U.S. and Israeli leaders - that "all options are on the table" in confronting Iran - was not enough to persuade Tehran to stop its uranium enrichment.
"I am sure that had there been three aircraft carriers with an American declaration that in the event the Iranians do not honor the Security Council decisions, the Americans are expected to attack by 2013, they would have acted differently," he said.
"Today the Iranians take into account that they have room to maneuver, and that is the most dangerous thing," he said.
Iran says its nuclear work is entirely peaceful and calls Israel's presumed atomic arsenal the bigger danger to the region.
Steinitz said Netanyahu had learned a lesson from Syria, where the world has stood largely by while over 100,000 people have died in two and a half years of civil war.
"It must be understood that no one will come to help us if, heaven forefend, we lose the ability to defend ourselves. Therefore we must do everything to prevent Iran from obtaining a nuclear weapon," he said.
Netanyahu is due to meet U.S. President Barack Obama in Washington on September 30 and has said that he wants to focus on Iran during the talks.
(Reporting by Ari Rabinovitch; Editing by Alison Williams)