The latest salvo in the seven-year war in Syria, an apparent chemical attack in the suburb of Douma at dusk on Saturday, has presented a new challenge to a Trump administration that has vowed to strongly respond.

But much is still unclear or unconfirmed about the attack, including what action the United States will take and what impact it will have on relationships with allies and adversaries. Syrian government forces prevent access to Douma for journalists, aid workers and investigators.

Here’s a brief look at what we know so far, and what remains to be seen as of Wednesday.

What we know

• About 500 people in Douma, a suburb of Damascus, had symptoms consistent with a chemical attack: burning eyes, breathing problems and white foam coming from their mouths and nostrils, according to several independent medical and rescue groups.

• Residents said they heard objects falling from the sky, followed by a strange smell that witnesses said resembled chlorine.