Aggressive Acts by Iran Signal Pressure on Its Leadership WASHINGTON - A string of aggressive gestures by Iran this week - assassination attempts on Israelis living abroad that were attributed to Tehran, renewed posturing over its nuclear program and fresh threats of economic retaliation - suggest that Iranian leaders are responding frantically, and with increasing unpredictability, to the tightening of sanctions by the West. As investigators unearthed new evidence implicating Iran in the attacks this week in Thailand, India and Georgia, President Mahmoud Ahmadinejad of Iran announced Wednesday what he said was his country's latest nuclear advance, and Iran's Oil Ministry threatened to pre-empt a European oil embargo by cutting off sales to six countries there. "These are all facets of the same message," said Muhammad Sahimi, an analyst and professor at the University of Southern California. "Iran is saying, "If you hit us, we will hit back, and we are not going to sacrifice our nuclear program." " The flurry of Iranian actions and statements comes as Western governments are watching closely for signs of Iran's reaction to the tougher sanctions they have imposed. But the intentions of Iran's divided leadership are notoriously difficult to divine, and even as Mr. Ahmadinejad declared defiantly that "the era of bullying nations has passed," another Iranian official said Tehran was ready for new talks on the nuclear issue. The European Union's foreign policy chief, Catherine Ashton, confirmed on Wednesday that she had received a reply from a top Iranian official responding to her invitation to negotiations over the future of its nuclear program. Iran's Al Alam television said the country had offered to "hold new talks over its nuclear program in a constructive way." American officials reacted with caution to the reported offer to talk and said they saw little substance in either the oil threat or Mr. Ahmadinejad's announcement that Iran had new centrifuges able to enrich uranium more quickly. The Iranian president was shown on live television overseeing the loading of what was described as an Iranian-made fuel rod into a research reactor and declaring that "the arrogant powers cannot monopolize nuclear technology. Victoria Nuland, the State Department spokeswoman, said that Mr. Ahmadinejad's remarks appeared "calibrated mostly for a domestic audience." "The Iranians have for many months been putting out calendars of accomplishments, and based on their own calendars, they are many, many months behind," Ms. Nuland said. Nor did the threat to cut oil sales to six European countries - first incorrectly announced by Iran's Press TV as already in effect - have much of an impact. The White House spokesman, Jay Carney, noted that the European Union banned new oil contracts with Iran last month and said it would halt all imports of Iranian oil July 1. Oil prices ticked up by $1.06 a barrel to $101.80 on the New York Mercantile Exchange in response to Iran's warning. Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace, said the belligerent moves by Iran actually underscored weakness. "If there's a meta-narrative here, it's that Iran tends to speak loudly but carries a small stick," Mr. Sadjadpour said. Their alleged terror attacks projected incompetence more than fear, their announced nuclear progress is likely exaggerated, and their threat to pre-emptively cease oil exports to Europe turned out to be another bluff. Evidence was accumulating that the bombing this week that injured four people in New Delhi, including an Israeli diplomat's wife, and bombs discovered in Tbilisi, Georgia, and Bangkok were part of a single plot, for which Israel has blamed Iran. Iranian officials have denied any involvement. Two Iranian suspects in the Bangkok episode - in which an explosion rocked a house and led investigators to more bombs there - were in custody in Thailand and a third in Malaysia, officials said. And Thailand's chief of police, Gen. Prewpan Dhamapong, said the explosive devices found in the rented house resembled those found in Georgia and New Delhi. In Israel, Prime Minister Benjamin Netanyahu said the incidents showed why all nations should draw "red lines against Iranian aggression." Reporting was contributed by Rick Gladstone and William J. Broad from New York, David E. Sanger from Washington, Thomas Fuller from Bangkok, Ethan Bronner from Jerusalem, and Alan Cowell from London.