ROME - Italy will consider its G8 meeting invitation to Iran rejected unless Tehran replies by the end of the day, the foreign minister said Monday in a sign of Rome's growing impatience.

Italy has invited Iran to attend talks on Afghanistan and Pakistan to be held during the Group of Eight foreign ministers' meeting starting Thursday in Trieste. Rome says Tehran could contribute to discussions on stabilizing the region.

Italy is Iran's leading trading partner in the European Union and has long maintained that no lasting solution in the Middle East conflict can be found without Tehran's involvement.

Rome kept its invitation to Trieste open even during the bloody crackdown on protests over Iran's disputed presidential election. As late as Sunday evening, a Foreign Ministry communique expressed the hope that Iran might make its contribution to the region at the Trieste meeting.

But on Monday, Foreign Minister Franco Frattini said that Iran must respond by the end of the day or "the invitation is to be considered implicitly rejected."

"Obviously there are rules in international diplomacy: When you invite somebody, that somebody has to respond," the minister said.

"Today there must be news in that respect," Frattini said on the sidelines of a conference in Rome. "We are G8 presidents, and frankly we cannot imagine we'll keep our hand extended for too long."

Frattini's spokesman, Maurizio Massari, said it would be difficult for Iran to focus on discussing stability in Afghanistan and Pakistan given its domestic turmoil -- saying that its potential contribution was the very reason why Iran had been invited in the first place.

The three-day meeting in the northeastern city of Trieste brings together the Group of Eight most industrialized nations and several other countries for wide-ranging talks.

U.S. Secretary of State Hillary Rodham Clinton is expected to attend, Massari said. The Quartet of key parties trying to promote Mideast peace -- the UN, the U.S., the European Union and Russia -- are also among the participants.

Reports of voting irregularities in the June 12 vote in Iran that re-elected hardline President Mahmoud Ahmadinejad have raised concerns in many European capitals, including London, Paris and Berlin.

Italy says there should be "a serious commitment by the Iranian authorities so that the outcome of the vote can reflect the real will of the Iranian people," according to Massari.

Rome has also defended European allies from Iran's accusations of foreign meddling, directed especially at Britain, France and Germany.

"European countries didn't manipulate anything," Frattini said. "We saw scenes of violence, and we believe there never should be violence," he was quoted as saying by the ANSA news agency.

The Foreign Ministry statement Sunday said Italy was "particularly concerned" and saddened about the loss of life in the street protests. It urged Iran to take urgent but peaceful measures to end the violence and hold an open meeting with the country's opposition.

Italy has instructed its embassy in Iran to provide humanitarian aid to the protesters wounded during the clashes, pending an EU-wide proposal to co-ordinate assistance. But so far the Italian Embassy has received no such requests for assistance, Massari said.