Diplomats from a dozen countries, led by the United States and Russia, are struggling to make progress in Syria, even as fighting in the north sends tens of thousands fleeing and threatens a deepening humanitarian crisis. Next month, Syria's civil war will reach the end of its fifth year, and its consequences continue to reach new and disastrous levels.

An AP News Guide to the latest events:

WAS A CEASE-FIRE AGREEMENT REACHED?

No. The U.S. and Russia and other nations agreed to try to work for a less ambitious goal: a pause in fighting or "cessation of hostilities," within a week. And even that vague formula will be difficult to pull off.

Moscow and Washington disagree over which armed factions would be covered under the cessation. Russia says it and its ally, the Syrian government, will continue to hit "terrorists," by which they mean not just the Islamic State group and al-Qaida's branch, the Nusra Front, but also a number of rebel factions opposing President Bashar Assad and backed by Saudi Arabia and Turkey. So that would effectively mean fighting would continue on many fronts even if a cessation is declared.

U.S. Secretary of State John Kerry lashed out at Moscow on Saturday, accusing it of "repeated aggression" in Syria and saying its warplanes were mainly targeting "legitimate opposition groups." Kerry insisted the conflict would not end without Assad's removal from power, a non-starter for the Syrian government and its allies.

ON THE BATTLEFIELD

Even as the diplomats debate in Europe, the shape of the battlefield is shifting rapidly. For two weeks, government forces have been on an offensive in the north, gaining ground in trying to encircle the rebel-held half of Aleppo, Syria's largest city before the war. The campaign has been helped by heavy Russian airstrikes, along with fighters from Lebanon's Hezbollah movement and members of Iran's Revolutionary Guard.

The fall of the rebel-held side of Aleppo would be the biggest blow to the opposition since the war began — and rebels believe Russia wants the fighting to continue as long as possible to allow troops to encircle and besiege the city. They're almost there: After capturing a string of villages to the north, including Tamoura on Saturday, government forces are poised to target the rebels' last remaining supply route to Turkey.

At least 300,000 people remain in the eastern, rebel-held half of Aleppo and face being cut off from aid. Tens of thousands have been fleeing the violence, compounding the humanitarian crisis.

HUMANITARIAN AID

The nations gathered in Munich agreed to accelerate humanitarian aid to besieged Syrian communities beginning this week. More than 1 million Syrians are estimated to be in towns and districts that have been blockaded for weeks or months, either by government forces or the rebels.

It is not clear how much aid will make it through without a real stop in combat — and each warring side must agree to open the way for the deliveries.

THE HUMAN COST

More than 250,000 people have been killed in Syria since 2011. Large parts of cities like Aleppo and Homs and suburbs outside of Damascus have been blasted into concrete husks by years of bombardment.

Half of Syria's prewar population of 22 million has been driven from their homes by the war, and the numbers continue to swell. Some 6.6 million have fled to other parts of Syria, and more than 4.6 million have left the country, overwhelming its neighbors, especially Turkey, Jordan and Lebanon.

A half-million Syrians were among the 1 million refugees who flowed into Europe in 2015, the biggest migration seen on the continent since World War II. Thousands continue to make the dangerous sea journey to Greece, hoping to find new lives in Europe.

The crisis has enflamed tensions among European Union members and beyond. Turkish leaders this week accused the EU of hypocrisy for pressuring them to both take in more Syrians and block them from entering Europe. Turkey already hosts some 2.5 million Syrians and said it is reaching the end of its capacity to take more, but tens of thousands fleeing the Aleppo fighting are massed on its border seeking to enter.

A REGIONAL WAR

With diplomats struggling to halt the fighting even temporarily, chances for a negotiated peace seem further than ever. All those players — directly or by proxy — complicate those efforts and make it effectively a regional war.

Assad is backed by his top allies: Russia, which began airstrikes against rebels in September, and Iran, which has given Damascus weapons and money and has sent its Revolutionary Guard forces to bolster his overstretched military. Also helping are Hezbollah guerrillas and Iraqi Shiite militias, which have been indispensable for battlefield victories.

The rebels get support from Saudi Arabia, Turkey, the United Arab Emirates and Qatar. The U.S. also backs some factions, but its efforts to train and arm an effective "moderate" rebel force have repeatedly floundered. Washington's emphasis has been more on fighting the Islamic State group, using an air campaign against the militants for more than a year in Iraq and Syria.

The Islamic State group has taken over a swath of Syria from the east up to the northwest, linked to its territory in neighboring Iraq. But it has lost ground in both countries because of airstrikes by a U.S.-led coalition and advances by Kurdish fighters.

The diplomacy is caught between the interests of those players. Moscow appears determined to help push Assad toward victory, or at least an improved position. The U.S. is caught between its priority of fighting IS and its allies' priority of bringing down Assad. Few seem willing to bend.

Saudi Arabia has talked of sending ground troops into Syria, and on Saturday, Turkey's Foreign Minister Mevlut Cavusoglu was quoted by local media as saying Ankara and Riyadh may mount a joint ground operation against IS in Syria. Syria's government has warned that any foreign ground troops entering the country would return home in "coffins."