"We call on the Iranian government to guarantee that the will of the Iranian people is reflected in the electoral process," the statement said.
David Miliband, Britain's foreign secretary, said: "I think there is unity here that it is for the Iranian people to choose their government but it is for the Iranian government to protect their people.
"The violence we have seen over the last 10 days and the killings and the beatings are deplorable and they show a failure to protect their own people.
"There is a crisis of credibility not between Iran and the West, but between the Iranian counting of the votes and the Iranian people."
The election results sparked protests in Tehran, the capital, that spilled into violent clashes between demonstrators and police and paramilitary forces.
Italy had invited Iran to attend the three-day gathering, arguing its presence could help efforts to stabilise Afghanistan, which was due to be the focal point of the meeting.
However, Rome retract its invitation following the clashes.
The EU commisioner for external relations condemned the use of excessive force and urged dialogue within Iran.
"I think it's a missed opportunity for the Iranian government," Benita Ferrero-Waldner said.
As the ministers opened the meeting, Franco Frattini, Italy's foreign minister, said the G8 was working on "a good document that would include condemnation ... but at the same time one that will recognise that electoral procedures are an Iranian question."
The statement is a compromise between countries that wanted to send a tough message to Iran over its suppression of mass street protests and use of violence and others, including Russia, who were careful to keep an avenue open for dialogue over Tehran's nuclear programme.
More than 20 people have been killed and many more imprisoned in the protests that followed Iran's election - the worst violence to sweep the country since 1979.
Iranian officials have accused two G8 members, Britain and the US, of inciting the protests and meddling with internal affairs.
Tehran has since said it is considering downgrading ties with Britain after it expelled two diplomats.
The UK followed suit by sending two Iranian diplomats home.
The G8 representatives, which also include France, Germany, Italy, Japan, Canada and Russia, started the gathering with a working dinner at the Palazzo della Regione in the city.
Sergei Lavrov, Russia's foreign minister said that Russia was not prepared to sign up to a G8 statement condemning the election itself.
"No one is willing to condemn the election process, because it's an exercise in democracy," he said.
Lavrov also suggested that overt condemnation would undermine the more important goal of addressing Iran's nuclear programme.
The meeting, which was initially scheduled to focus on stabilising Afghanistan and moving the Middle East peace process forward, is also meant to lay the groundwork for the G8 summit in two weeks in L'Aquila, the central Italian city devastated by an earthquake in April.