Major powers agreed to a cessation of hostilities in Syria and to expand delivery of humanitarian aid to people caught up in the conflict, top diplomats said in Munich on February 12.

U.S. Secretary of State John Kerry, speaking to reporters after an hours-long meeting with envoys from Russia and more than a dozen other countries in the Syrian Support Group, said the target for implementing the nationwide end of fighting was a week's time.

He said all participants had agreed that formal negotiations to establish a more lasting peace on Syria should resume in Geneva as soon as possible.

Kerry called the agreed-on truce a "pause," not a "cease-fire," which he said would be "far more permanent -- an end of conflict."

"The objective is to achieve a durable long-term cease-fire at some point in time" but that can only come through "genuine negotiations," Kerry said, adding that the commitments made in Munich are only "on paper" and need to be borne out in practice.

The truce would not apply to Islamic State, Al-Nusra Front, which is Al-Qaeda's Syrian affliate, and other extremist groups, he said.

British Foreign Secretary Philip Hammond said the agreement could only be considered a "breakthrough" it if succeeds in stopping Russia from supporting Syrian government forces with air strikes as they advance against opposition strongholds in Aleppo.

"If implemented fully and properly...this will be an important step towards relieving the killing and suffering in Syria," Hammond said. "But it will only succeed if there is a major change of behavior by the Syrian regime and its supporters."

Kerry and Russian Foreign Minister Sergey Lavrov said the United States and Russia would co-chair both a new working group on humanitarian aid in Syria as well as a group establishing the "modalities" of the temporary truce.

While humanitarian access is critical to relieving the suffering of millions of Syrians, a cease-fire will be required if stalled negotiations between Syrian President Bashar Assad's government and the opposition are to resume by the UN's target date of February 25.

Peace talks broke down on February 3 before they really started, due largely to gains by Assad's military in Aleppo province with the heavy backing of Russian air strikes, gains which have continued to the present day.

Thorny issues that stymied earlier negotations remain unresolved, including which groups besides Islamic State and Al-Nusra should be considered terrorist and excluded from the peace negotiations.

Russia and Syria contend that groups they are fighting in Aleppo, some of which are supported by Turkey, Saudi Arabia and the West, are in the terrorist category.

Lavrov on February 12 said the Russian air campaign in support of Assad's military would continue against such terrorist groups, suggesting that Moscow could continue to justify bombings in Aleppo citing the "terrorist" exception to the truce.

Much is at stake in the latest attempt to end the nearly five-year civil war in Syria. Russian Prime Minister Dmitry Medvedev on February 11 raised the spectre of an interminable conflict or even a world war if the peace talks fail, given open discussion by the United States and Saudi Arabia of sending ground troops to join in the conflict.

Even without such escalation, the damage from the war has been monumental, with hundreds of thousands of people killed, the spawning of Europe's biggest refugee crisis since World War II, and the rise of the Islamic State, which declared an Islamic caliphate on territory it carved out in Syria and Iraq.

With reporting by Reuters, AP, AFP, and dpa