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.