WASHINGTON, June 18 (Xinhua) -- The top priority of the upcoming G-20 summit in Toronto "must be to safeguard and strengthen the recovery," U.S. President Barack Obama said.

"We worked exceptionally hard to restore growth; we cannot falter or lose strength now," the president wrote in a letter to G-20 leaders that was made public Friday.

"This means that we should reaffirm our unity of purpose to provide the policy support necessary to keep economic growth strong," Obama said.

Obama said that during the June 25-27 gathering in Toronto the G-20 leaders "meet at a time of renewed challenge to the global economy."

"It is essential that we have a self-sustaining recovery that creates the good jobs that our people need," he said.

The G-20 leaders should be prepared to respond again as quickly and as forcefully as needed to avert a slowdown in economic activity if confidence in the strength of the world recovery diminishes, he added.

Obama said that when the G-20 leaders met in London in April 2009, the world was facing the worst global financial crisis since the 1930s.

Leaders acted with unprecedented speed and aggressive action to boost demand and repair the financial systems, he said. "It worked."

In Pittsburgh in September 2009, with recovery beginning to take hold, G20 leaders agreed to work together to achieve a more balanced pattern of global growth and financial reforms to strengthen financial system and protect economies from instability.

Also at the Pittsburgh summit, leaders agreed to make G-20 the prior platform of global economic coordination.

Obama said that it is important that in Toronto the G-20 demonstrates its continued determination to work collectively to address the renewed challenges facing the global economy.

"We need to commit to restore sustainable public finances in the medium term. And we should complete the work of financial repair and reform," he said.

Although the global economic recovery is on track, it remains fragile. The ongoing European debt crisis has been casting shadows over the global economic prospect.

The G-20, which includes the United States, Canada, major European nations, Japan, China, India and other influential developing countries, will meet next week in Toronto to discuss critical issues of the world economy.

It will be the fourth meeting of G-20 leaders since their first gathering in Washington in November 2008 when the global financial crisis was at its height.