Jim Michaels

USA TODAY

The United States and Russia said early Saturday in Geneva they had reached a landmark agreement that would lead to a cease-fire in the five-year-old Syrian civil war and pave the way for broader military cooperation in the battle against the Islamic State and al-Qaeda terrorists.

Secretary of State John Kerry called the deal a potential "turning point" in the bloody conflict, which has caused hundreds of thousands of deaths and forced millions to flee their homes. Kerry and Russian Foreign Minister Sergey Lavrov announced the agreement in Geneva, Switzerland where negotiators hammered out the deal.

"Working together, Russia and the United States and our teams have devised what we think is a more proscriptive and far-reaching approach than we have been able to put together to date," Kerry said in a press conference. "If the plan is implemented in good faith, if the stakeholders do the things that are available to them to do and are being called on to do, this can be a moment where the multilateral efforts at the diplomatic table, the negotiations could take hold, and you could really provide the people of Syria with a transition."

The cease-fire is set to begin at sundown on Monday. It is seen as a first step in what could become a broader military pact between Russia and the United States that has so far remained elusive.

Citing a number of recent meetings with Lavrov, Kerry said: "The United States is going the extra mile here because we believe that Russia, and my colleague, have the capability to press the Assad regime to stop this conflict and to come to the table and make peace."

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"This is just the beginning of our new relations," Lavrov said. "We hope that all those who dearly value peace and the integrity of the multinational and multi-confessional Syrian state will support our arrangements.

There are still formidable obstacles in the way of carrying out the agreement. Hundreds of factions are fighting in Syria and getting them all to cooperate will be a challenge. A previous ceasefire agreement in Syria collapsed.

This deal appears more ambitious, since it includes an agreement to seek broader military cooperation between Russia and the United States if the ceasefire holds.

The Pentagon said that a "cessation of hostilities" would have to hold for seven days before the broader military cooperation would go into effect.

"We will be watching closely the implementation of this understanding in the days ahead," Pentagon Press Secretary Peter Cook said in a statement. The Pentagon has been wary of Russian military actions in Syria.

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Lavrov said Syrian President Bashar al-Assad is willing to comply with the agreement, according to the Associated Press.

"The Syrian Government has been informed by us about these arrangements, and it is ready to fulfill them," Lavrov said in a press conference. "It supports the initiative on which we agreed with United States, so we will do everything which depends on us, but it is understandable that not everything depends on us."

Russia and the United States are both conducting military operations in Syria. The Pentagon is backing local ground forces and conducting airstrikes against the Islamic State.

Russia is also conducting airstrikes, but Washington has accused it of carrying out operations aimed at propping up the Assad regime by striking members of U.S.-back moderate opponents of the Syrian president. The United States wants Assad to step down because of his brutal attacks on civilians with chemical weapons and other armaments.

Russia and the United States have agreed to hold regular talks aimed at ensuring aircraft remain at safe distances from each other, but are not cooperating on military operations.

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A broad agreement to cooperate could mean the two sides would eventually share intelligence and agree on which targets to strike. UN Special Envoy Staffan de Mistura praised the efforts and hopes the agreement will lead to a peaceful resolution in Syria

"The United Nations stands ready to deliver and to do whatever it can to support an early restoration of the cessation of hostilities," de Mistura said in the press conference. "It also expects that all parties will facilitate UN efforts to indeed deliver humanitarian assistance to the population in need, including in besieged and hard-to-reach areas