The EU foreign policy chief and Iran's nuclear negotiator have held talks on calls for a halt to Iranian uranium enrichment, without any breakthrough.
The two negotiators met last week for a working dinner
The EU's Javier Solana had been pressing Ali Larijani to accept an offer of incentives aimed at suspending Tehran's enrichment programme.
But Mr Larijani said the offer contained too many "ambiguities" for Iran to give a response.
A spokeswoman for Mr Solana described the meeting as "disappointing".
The EU had been hoping for a "substantial response" from the Brussels meeting, and the US secretary of state has also urged Tehran to respond to the offer.
But Iran insists it will make no final decision before August.
"We must be patient and try to negotiate...We must allow more time for negotiations to work," Mr Larijani said after his four-hour meeting with Mr Solana.
Foreign ministers of the five permanent UN Security Council members plus Germany are to meet in Paris on Wednesday to discuss their next move.
"We will make (an) analysis and we will see how to proceed," Mr Solana said.
Neither man gave any further details of the talks to reporters, but they said they would be in contact after Mr Solana had reported to Wednesday's meeting.
Iran allowed to buy spare parts for civilian aircraft made by US manufacturers
Restrictions lifted on the use of US technology in agriculture
Provision of light water nuclear reactors and enriched fuel
Support for Iranian membership of World Trade Organisation
From Western diplomatic sources
Mr Solana said they had reviewed events since his delivery of the UN offer of economic and political incentives to Tehran, during a visit to the Iranian capital on 6 June.
Neither side gave an indication on whether Iran was moving toward accepting the package, which is backed by the five permanent members of the UN Security Council and Germany.
Although no formal deadline was imposed, US President George W Bush later said the Iranians had "weeks not months" to respond to the offer.
The US wants Tehran to respond to the offer before the start of the G8 summit on Saturday.
Speaking in Washington before the meeting, US Secretary of State Condoleezza Rice had said it was time for Tehran to respond to the offer.
The US had previously championed diplomatic censure of Iran from by the UN Security Council.
However, Iran's foreign minister had said Tehran saw Tuesday's talks in Brussels as a chance to iron out some details in the proposal, rather than a time to make a final decision.
Iran denies claims it is trying to make atomic bombs and insists it has a right to enrich uranium for civilian purposes.