Iran has confirmed that it will not sign up to tougher, short-notice inspections of suspected nuclear sites.
Iran says it has nothing to hide
The European Union joined growing international pressure on Iran on Monday, saying Tehran should comply with the measures "urgently and unconditionally".
The International Atomic Energy Agency (IAEA) has also urged Iran to agree to strengthened inspections under an additional protocol to the Nuclear Non-Proliferation Treaty (NPT).
But Iran said a ban on the country's access to nuclear technology would have to be lifted before it can agree to such a move.
The head of the IAEA, Mohammed ElBaradei, said Iran had failed to report some of its nuclear activities - an accusation Tehran rejects.
UK Foreign Secretary Jack Straw, for his part, urged Iran to meet its non-proliferation obligations, as it continues trade negotiations with the European Union.
Allows for inspections at short notice
IAEA can take environmental samples at any location
So far EU foreign ministers have stopped short of backing US accusations that Iran has a secret nuclear weapons programme.
Iran has repeatedly said the aim of its programme was to generate electricity.
An Iranian representative at the IAEA in Vienna said the nuclear issue had been "politically motivated and politically charged", but would be resolved.
In Tehran, a spokesman for the country's Atomic Energy Organisation said Iran was studying the call to sign an additional protocol "with a positive view".
He said Tehran might agree to sign it, but reiterated Iran's demand for access to nuclear technology in exchange.
However analysts say this has already been ruled out by the US and other countries.
Mr ElBaradei urged the Iranians to sign the protocols unconditionally.
He said Tehran's co-operation would enable the IAEA "to provide credible assurances regarding the peaceful nature" of the country's nuclear programme.
Some EU countries want trade talks with Iran halted, but a majority believe the EU should keep the door open to dialogue, as a means of obtaining greater transparency on nuclear issues and more progress on human rights and political reforms in Iran.
The EU meeting came a few days after an IAEA report on Iran was leaked.
It says Tehran has failed to:
Mr ElBaradei visited Iran in February, and toured a nuclear plant under construction at Natanz, 320 kilometres (200 miles) south of Tehran.
Account for nuclear material
- Provide documentation for imports of nuclear material
Report its subsequent processing and use
Declare facilities where the material is stored and processed
The site is crucial, because it is where Iran is developing a series of centrifuges, which could be used to produce enriched uranium - the material used for making a nuclear bomb.
The IAEA reports says that Iran's failure to provide information in a timely manner has become "a matter for concern".