The ruling Socialist Party which Gonzalez led in government from 1982 to 1996 dismissed opposition criticism of the visit, insisting it was designed to underpin EU attempts to foster a wider dialogue.

Socialist Party parliamentary spokesman Diego Lopez Garrido told Cadena Ser radio the former leader was merely adding to that dialogue and "therefore, there are no grounds to see anything negative" in the visit.

The main conservative opposition Popular Party (PP) had earlier criticised Gonzalez's visit, given the green light by Madrid.

The PP's head of international relations, Gustavo de Aristegui, slammed the trip as "inopportune and irresponsible."

Centre-left newspaper El Pais, close to the Socialist government, reported that "Gonzalez undertook mediation between Tehran and Washington" at the former's request, and showed him shaking hands with Ahmadinejad.

El Pais said he was "working to bring closer the positions of Tehran and Washington" and pointed out that Gonzalez discussed the issue with US Secretary of State Condoleezza Rice last May.

Gonzalez also met Iran's chief nuclear negotiator, Ali Larijani, as Tehran repeated that it would not relinquish its "right" to nuclear energy in its first reaction to a critical International Atomic Energy Agency (IAEA) report.

Iran denies allegations by the United States and others that its nuclear energy programme is a cover for efforts to build nuclear weapons.

An editorial in Friday's conservative daily paper El Mundo opined that "Spain is playing with fire in Iran" and noted that Gonzalez had defended "the right of the Iranian people to acceed to nuclear technology."

Gonzalez, writing in El Pais, meanwhile addressed the issue of the Middle East conflict in calling on EU states to undertake what he called a "strong initiative" which could bring about a "definitive" peace settlement.

Spain was later Friday to unveil the size of its contribution to the multinational peacekeeping force in Lebanon.

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