Iran has resisted UK pressure to open up its nuclear sites to tougher inspections, saying it would expect "positive steps" in return.
Straw (left) told Iran that trade ties might be harmed
"We are ready for talks and co-operation. But Iran's transparency should be reciprocated," Iranian Foreign Minister Kamal Kharrazi said.
He was speaking at a joint press conference in Tehran with his UK counterpart Jack Straw, who earlier warned him the issue could affect Iran's relations with the European Union (EU)
There is growing international concern that Iran might be developing nuclear weapons, despite Tehran's insistence that it is only interested in atomic energy for peaceful purposes.
The UN nuclear watchdog, the International Atomic Energy Agency (IAEA), wants Iran to sign an additional protocol to the Nuclear Non-Proliferation Treaty (NPT), which will allow more intrusive inspections of Iran's nuclear sites.
Ties with EU
Echoing US concerns, Mr Straw said Britain and the EU wanted to see progress in the areas of human rights and inspections of Iran's nuclear facilities, otherwise trade talks between the EU and Iran could suffer.
The BBC's Jim Muir in Tehran says the trade carrot is an important incentive for Iran, which wants to cultivate ties with Europe as a counter-balance to the US.
Iran has detained students who staged anti-government protests
Mr Kharrazi said Iran was committed to co-operating with the IAEA, but it expected a positive response.
"When Iran signs the protocol, others should also take positive steps," he said.
On the issue of terrorism, Mr Kharrazi indicated that Iran was also seeking a quid pro quo to hand over a number of al-Qaeda suspects it admits it is holding.
Our correspondent says the minister was implying that Iran wanted the UK and America to crack down on an Iranian opposition faction, the People's Mujahideen, in Iraq.
It is Mr Straw's fourth visit in less than two years to Iran, which has been dubbed part of an "axis of evil" by US President George Bush.
Despite the close relationship between Britain and the US, the UK's policy of "constructive dialogue" with Tehran stands in marked contrast to the United States' calls for the international community to isolate the Iranian regime.
Mr Straw is due to meet Iranian President Mohammad Khatami on Monday.
Anger at UK
Mr Straw's visit coincides with heightened political tensions in Iran, where there has been weeks of anti-government protests by Iranian students.
Mr Kharrazi told Mr Straw that the Iranian Government was deeply dissatisfied with remarks by UK Prime Minister Tony Blair in support of the demonstrators.
The foreign minister said he would expect Mr Blair to make a distinction between peaceful demonstrators and vandals who destroyed public property.
Four members of the Iranian parliament, meanwhile, have ended a sit-in called in protest at the arrest of a number of student demonstrators.
They accepted a pledge that the detained students would be handed over to the intelligence ministry, rather than be questioned by the hardline judiciary.