Top Iranian and EU negotiators will meet Thursday night for an informal discussion of Tehran's response to the international incentives package designed to defuse the standoff with the West over its nuclear program, officials from both sides said. "Tonight (EU foreign policy chief Javier) Solana will have a tete-a-tete dinner with Ali Larijani, to get the first response from the Iranians to the international offer," EU spokeswoman Cristina Gallach said. Larijani is Iran's top nuclear negotiator. His scheduled meeting with Solana on Wednesday - at which he was supposed to respond to the package submitted to Iran last month - was called off at the last minute and rescheduled for Thursday. Iran cited anger over the activities of exiled opposition groups as the reason for the unexpected delay. Gallach said the two delegations will meet again next Tuesday in Brussels to formally address the issue. Iranian officials have said they will seek explanations for "ambiguities" contained in the offer put forward by the United States, Russia, China, Britain, France and Germany. The package - which includes incentives such as nuclear expertise and reactors - calls on Iran to suspend enrichment for the duration of any negotiations, and sets out the priority of a long-term moratorium of such activity until the international community is convinced that Iran's nuclear aims are peaceful. In Tehran, Javad Vaeidi, another nuclear negotiator, confirmed that Larijani and Solana had decided to meet privately on Thursday. Vaeidi told state television the full delegations would hold official talks next Tuesday in Brussels. Western diplomats have threatened to restart efforts to punish Iran through possible UN Security Council sanctions unless Tehran stops enrichment and agrees to talks by July 12 when foreign ministers of the five permanent Security Council nations and Germany consult in Paris. In Washington Wednesday, US Secretary of State Condoleezza Rice said Iran needed to give "a substantive response" to a Western overture meant to end the crisis before the Group of Eight leaders meet later this month in St. Petersburg, Russia. "If indeed Iran is trying to stall, it's not going to work," Rice told reporters. "The international community has said that we need to get an answer, an indication of where Iran is going with this. We need to know if the path of negotiation is open or not." Earlier this week, EU officials said they did not anticipate Larijani would fully respond to the offer, but only to seek clarification of several points of the package _ and perhaps to come up with a counterproposal. Tehran has asserted repeatedly that its nuclear program, which includes uranium enrichment, is peaceful and aimed at generating power. But the U.S., Israel and EU fear the research program is a cover for the development of nuclear weapons. Work on a Security Council resolution was suspended May 3 to allow the six powers to draw up the plan of perks if Iran agrees to a long-term moratorium on enrichment - or punishments that include the threat of selective UN sanctions if it does not. Possible UN-mandated sanctions include a visa ban on government officials, freezing assets, blocking financial transactions by government figures and those involved in the country's nuclear program, an arms embargo and a blockade on the shipping of refined oil products.