The grouping, which was earlier known as Group of Seven (G7), has met annually for more than 30 years. It consisted of the largest developed economies: Britain, Canada, France, Germany, Italy, Japan and the US. In 1997, Russia formally joined them, making it the Group of Eight (G8).

Leaders said the G20 would become the 'premier forum for their international economic cooperation'. Leaders have long pledged to keep the G7 and G8 as a place to discuss security issues.

German Chancellor Angela Merkel said she was satisfied with the compromises reached so far in the G20 summit to rein in the risky practices of financial firms in future.

The G20 talks were overshadowed by Iran's admission that it had a second nuclear facility. Obama, British Prime Minister Gordon Brown and French President Nicolas Sarkozy appeared together Friday to condemn the development, before heading into their G20 meetings.

Obama called it 'disturbing' and said the size of Iran's second nuclear plant was 'inconsistent' with use for civilian power. US officials alleged its sole purpose was to give the Islamic state the option to produce material for atomic weapons.

The G20 summit led to scattered protests in parts of Pittsburgh as the meeting opened with a dinner Thursday night. More than 4,000 police have been mobilised for the summit in the city of about 300,000.

European Union officials warned that little progress was being made on narrowing differences on climate change. EU Commission President Jose Manuel Barroso said Thursday that efforts to reach a new global climate treaty by a December summit in Copenhagen were in jeopardy.

Leaders of the G20 first met in November 2008 in Washington in the wake of the financial crisis that started in September on Wall Street and gathered again in London in April this year.