British Foreign Secretary William Hague has hailed the agreement reached between the P5+1 group and Iran on the latter's nuclear program as "important and encouraging first stage agreement."

After days of intensive negotiations, Iran and the six countries -- Britain, France, Russia, China, the United States and Germany (P5+1) have reached a first-step agreement on its nuclear program, EU foreign policy chief Catherine Ashton announced early Sunday morning.

Writing on his Twitter, Hague said that the agreement with Iran is good for the whole world, including Middle Eastern countries and the people of Iran themselves.

"This agreement shows it is possible to work with Iran, and through diplomacy address intractable problems," the foreign secretary said.

"Negotiations were painstaking. Tomorrow hard work begins of implementing and building on the agreement," he said.

U.S. President Barack Obama hailed the deal as "an important first step toward a comprehensive solution" to Iran's nuclear program and "the most significant and tangible progress" ever made since he took office.

The president acknowledged Iran's right to peaceful use of nuclear energy as he said "we approach these negotiations with a basic understanding: Iran, like any nation, should be able to access peaceful nuclear energy."

"We will refrain from imposing new sanctions, and we will allow the Iranian government access to a portion of the revenue that they have been denied through sanctions," Obama said.