All eyes on Syria as U.S. weighs military strike: Here's the latest

Show Caption Hide Caption AP explainer: Trump weighs Syria attack reaction WARNING: This contains graphic photos of the attack. AP National Security Writer Robert Burns lays out the range of options the Trump administration has available to it in response to the Assad regime's reported use of chemical weapons in Syria.

The world awaited President Trump's response Wednesday to the alleged chemical weapons attack by Syrian President Bashar Assad on civilians in a rebel-held suburb of Damascus.

Syria was bracing for a military strike that could be larger than a year ago, when Trump ordered an assault on the war-battered Middle Eastern nation's chemical warfare assets.

The rebel Syria Civil Defense Force claimed more than 40 people were killed and entire families were gassed to death in Saturday's attack by Assad's forces on the town of Douma. Syrian troops have often been accused of using chemical agents during the nation's devastating, seven-year civil war.

Trump has also blamed Russian President Vladimir Putin and Iran for providing support to Assad. Asked if Putin bears responsibility, Trump has said that "if he does, it's going to be very tough, very tough ... Everybody's going to pay a price. He will, everybody will."

What might a military strike look like?

The Pentagon is likely planning a larger strike than what U.S. warships launched on April 7, 2017, in response to the Assad regime’s use of chemical weapons, said a former senior Defense official familiar with planning for that attack. Last year, 59 Tomahawk cruise missiles targeted Syrian warplanes suspected of carrying out the chemical assault. Pentagon planners now are also likely to target the pilots and the commanders, said the former official who spoke about military options on condition of anonymity.

What does Syria say?

The Syrian Foreign Ministry has repeatedly denied using chemical weapons, calling the claims a pretext for a military attack. The "reckless escalation" by the U.S. is no surprise from a country "that has sponsored and is still sponsoring terrorism in Syria," the ministry said.

What did Russia say?

Russia has denied chemical weapons were used. And Alexander Zasypkin, Russia's ambassador to Lebanon, vowed that any missiles fired at Syria would be shot down and the launch sites attacked.

How did Trump respond to Russia?

"Russia vows to shoot down any and all missiles fired at Syria," Trump tweeted early Wednesday. "Get ready Russia, because they will be coming, nice and new and “smart!” You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!" Trump also blamed the deteriorating U.S.-Russia relationship on the "Fake & Corrupt Russia Investigation, headed up by the all Democrat loyalists."

More: Trump isn't ruining the 'element of surprise' with Syria threats, experts say

Did Russia respond to Trump's tweet?

Russian Foreign Ministry spokesperson Maria Zakharova posted on Facebook that "Smart missiles should fly toward terrorists, not the legitimate government that has been fighting international terrorism for several years on its territory." She also said the strikes could destroy evidence needed to determine if chemical weapons were used in Saturday's attack.

More: Trump warns Russia, saying missiles 'will be coming' in Syria

Would U.S. allies join in the fight?

British and French forces are expected to take part in the response to Assad’s use of chemical weapons, the former Pentagon official said. French president Emmanuel Macron called for a strong, joint response to the alleged chemical attack. He said any strike would target the Syrian government's chemical weapons capabilities, adding he did not want "an escalation" of the war. British Prime Minister Theresa May has not said whether British forces would be involved.

More: Syria conflict explained: What's at stake after latest gas attack

Has the United Nations become involved?

The U.S. has asked the United Nations Security Council to authorize an independent inquiry. United Nations Secretary-General Antonio Guterres on Tuesday also called for an investigation, saying he was "outraged" by reports of chemical weapons use.

Will an inquiry take place?

Syria invited the Organization for the Prohibition of Chemical Weapons, a respected global watchdog, to conduct an investigation. The organization said it will "soon" send a fact-finding team to Syria.

Had Trump planned to pull advisers out of Syria?

The United States has about 2,000 troops on the ground in Syria to support local militias fighting the Islamic State. Less than two weeks ago, Trump said he wanted to bring U.S. troops home from Syria. The White House, however, quickly signaled that a U.S. withdrawal is not imminent. Still, Sen. John McCain, R-Ariz., chairman of the Senate Armed Service Committee, said Trump's "premature" declaration emboldened Assad.

How did we get here?

The civil war aimed at ending Assad's authoritarian rule has dragged on for more than seven years and cost more than 400,000 lives, according to United Nations estimates. The U.S. mission is to support local militias fighting the Islamic State, but the U.S. has avoided clashing with Assad's armed forces or their Iranian and Russian backers.