Obama uses G8 debut to issue warning to Iran

* Obama: Iran faces September timeframe on nuclear issue

* U.S. president says door still open to diplomacy



By Matt Spetalnick

L'AQUILA, Italy, July 10 (Reuters) - U.S. President Barack Obama warned Iran on Friday the world will not wait indefinitely for it to end its nuclear defiance, saying Tehran had until September to comply or else face consequences.

Obama, speaking at the end of a G8 summit in Italy, said leaders had sent a message condemning the "appalling" events surrounding Iran's disputed presidential election and expressing solidarity against Tehran's nuclear ambitions.

He said he hoped Iran would enter negotiations on the issue and that leaders would review the situation again at a G20 meeting of developed and developing countries in Pittsburgh in September.

"If Iran chooses not to walk through that door, then you have on record the G8, to begin with, but I think potentially a lot of other countries that are going to say we need to take further steps," Obama told reporters.

"We also say we're not going to just wait indefinitely and allow for the development of a nuclear weapon, the breach of international treaties, and wake up one day and find ourselves in a much worse situation and unable to act," he said.

Obama made clear he was sticking to his strategy of trying to engage Iran diplomatically, a departure from his predecessor George W. Bush, who pursued a policy of isolation.

But Obama's approach has been complicated by Iran's June 12 presidential election, in which President Mahmoud Ahmadinejad was declared the victor by a wide margin and security forces cracked down violently on protesters who claimed voting fraud.



SHARPER LINE

Obama, who sharpened his line against Tehran after being criticized at home for a cautious approach in the election aftermath, wanted to forge a united front at the summit.

He said that he and others had sought only the strong condemnation that the G8 delivered and not for the summit to embrace new sanctions against Iran, despite news reports to the contrary.

But it remained unclear what further pressure could be exerted on Tehran, which has rejected international demands to suspend a nuclear program the West believes is for developing weapons but which Tehran says is for electricity generation.

Though Russia signed up to the G8 statement, it has usually been reluctant to tighten sanctions on Iran, a key trading partner and arms customer.

Iran figured prominently on the agenda of Obama's first G8 summit, but three days of talks also focussed heavily on climate change.

Having pledged to lead the fight against climate change, Obama helped secure agreement by major economies to back a goal of limiting global warming to no more than two degrees Celsius (3.6 Fahrenheit) over pre-industrial levels.

But the Group of Eight rich nations failed to persuade top emitter China and India to join in a push to reduce global greenhouse gas emissions by 50 percent by 2050 -- a blow to efforts to secure a new U.N. pact by year end.

Diplomats said Obama had led a push for the G8 to up its pledge of farm aid for poor nations to $20 billion, surpassing expectations of how much would be offered.

The aid announcements came just hours before Obama was due to head to Ghana on his first visit to sub-Saharan Africa since he was elected the first black U.S. president. (Additional reporting by Jeff Mason and Gavin Jones; editing by Patrick Graham)