Shortly before dawn local time on Tuesday, the US began launching air strikes in Syria against the jihadist group Islamic State in Iraq and Syria (ISIS), as part of President Obama's effort to "degrade and defeat" the group that has seized vast parts of both countries and beheaded two American journalists.

This is a major escalation for the US, which has avoided direct engagement in Syria's civil war since it began in 2011. But it is also shrouded in a degree of mystery, with the details of the strikes, its targets, and its implications for the Middle East not totally clear. Here, then, is a running account of what we know and don't know.

What we know

— The air strikes and cruise missiles hit ISIS in four Syrian cities, including the northern Syrian city of Raqqa, the group's self-declared headquarters. They also hit the ISIS strongholds of Dair Elzur, Hasakah, and Abu Kamal.

— The Pentagon says the strikes against ISIS destroyed "fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance center, supply trucks and armed vehicles."

— Five Arab countries also participated in the operation: four Gulf countries — Saudi Arabia, Qatar, Bahrain, and the United Arab Emirates — and Jordan. Saudi participation is big deal here, as the Saudis have been hesitant to act so fully against ISIS (they share a mutual enemy, Bashar al-Assad) and are a regional power.

— The US notified Syria that it was going to strike ISIS. The Syrian government did not grant formal permission for the strikes in its territory, but these attacks help Bashar al-Assad, who is also at war with ISIS. Assad's air defense system is conspicuously declining to fire on the American and Arab jets.

— This is a huge success for Bashar al-Assad. The Syrian leader has now convinced the world's most powerful country, which was threatening to bomb him just a year ago, to instead bomb his enemies. There is a strong indication that this was his plan all along.

— The US also bombed the al-Qaeda branch in Syria, Jabhat al-Nusra. The strikes reportedly killed over 50 al-Qaeda militants, most of them foreign fighters; the group is an enemy of ISIS.

— US strikes also hit an al-Qaeda group called Khorasan. The little-known group, which some analysts say is actually just a collection of al-Qaeda officers, is said to have been plotting an attack on the US.

— An unknown number of civilians were killed in the strikes. Syrian rights groups say the civilian casualties include three children.

— Israel shot down a Syrian military jet over its territory. This is the first time this has happened in 25 years; Syria also acknowledged the incident. An Israeli spokesperson said, "We had to shut him down even though we understand that his intention was not to attack us."

What we don't know

— How will ISIS respond? The group has beheaded two American journalists, as well as a British aid worker and a number of Lebanese citizens. The group seemed to be inviting American air strikes; now that they are occurring, they is no telling for sure how the group will respond.

— Is the US coordinating with Assad? The US government insists there is zero direct cooperation with Syria's government, but Syria says that Secretary of State John Kerry sent them a secret letter explaining their actions and has hinted at a degree of implicit cooperation. Syria's claims may well be a lie designed to make Assad look less powerless, but there is certainly implicit cooperation as American and Syrian forces are avoiding shooting at one another.

— Why did the Syrian jet cross into Israel? This is an extremely bizarre and perplexing incident, given that the Syrians had to know how Israel would respond. Was it an accident? A response to some clandestine Israeli action? Is it related to the US-led bombing, or entirely separate?

— What is the Khorasan group? Many terrorism analysts doubt the US government claims that this is a shadowy, scary new group plotting against the US, saying it is simply a collection of al-Qaeda veterans from Afghanistan. How distinct is the group, really? Is it actually plotting against the US, and how credibly? And how accurate are the reports that the US strikes killed senior Khorasan leaders during the strikes?

— Will moderate Syrian rebels be able to push back ISIS now? Many analysts doubt bombing alone will be enough to push back ISIS. The US is upgrading its support to so-called moderate rebels, but it's not clear if this will be enough, or whether those rebels will willingly turn their guns from Assad toward ISIS.

— Will Assad finally confront ISIS? There is wide suspicion that Assad allowed ISIS to grow, or even fostered their rise, because he knew it would lead the US to attack them, implicitly taking his side. Will he now finally unleash the Syrian military on ISIS?

— What is Iran's role? Iran is openly backing the Syrian government against ISIS, and the US and Iran have hinted at cooperating against ISIS in Iraq, where they have more or less the same agenda. But Iran supports Assad, while the US wants to undermine him. So it's not clear how their missions and actions — and possible coordination — will line up in Syria.

— Will other American allies participate in the Syria bombing campaign? After the bombings began, a UK spokesperson said that "supports the latest air strikes against ISIL terrorists which have been carried out by the US and 5 other countries from the Gulf and Middle East," implying the UK was not, as yet, participating in direct military action. However, the spokesperson also said that "the UK is already offering significant military support, including supplying arms to the Kurds as well as surveillance operations by a squadron of Tornadoes and other RAF aircraft." Whether that kind of support from the UK or other non-Arab partners escalates to the use of force remains unclear.

— Has ISIS started operating inside Jordan? A spokesperson for the Jordanian government reportedly told CNN it had, and that this was why Jordan had participated in the strikes. But that justification has not yet been stated elsewhere, and despite previous reports of ISIS infiltration in Jordan, the scale and risk of the group's activities there are not yet clear. Still, any ISIS presence in Jordan would likely alarm its closest allies, the US and Saudi Arabia

The US is bombing Syria to destroy ISIS. Here's why that almost certainly won't work, explained in 2 minutes: