ROME, June 22 (Reuters) - Italy said on Monday that Iran appeared to have rejected an invitation to this week's Group of Eight foreign ministers meeting, after a deadline passed for Tehran to signal its participation.

Foreign Minister Franco Frattini had given Iran's government, facing street protests over this month's contested presidential election, until the end of Monday to accept the invite to the summit in the northern Italian port of Trieste.

"With three days to go, I still do not have a reply: I must consider that Iran has declined the invitation," Frattini, who will host the summit, told Italian television. "Iran has lost an opportunity by not participating in the conference."

The three-day Trieste meeting, which opens on Thursday, is due to discuss means of bringing greater stability to Afghanistan, which shares a long western border with Iran.

But delegates from the world's main industrial powers are also expected to discuss the unrest in Iran.

Tehran's relations with the West have been shaken by the protests following the re-election of hardline President Mahmoud Ahmadinejad. Iranian authorities have accused Western powers of supporting the street protests -- the most widespread since the 1979 Islamic Revolution. (Reporting by Valentina Consiglio; Editing by Jon Boyle)

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