By ROBERT BURNS and CATHERINE LUCEY
Associated Press

WASHINGTON (AP) - Russia and Britain exchanged sharp accusations Friday over the suspected poison gas attack in Syria, and the U.S. Navy was moving an additional Tomahawk missile-armed ship within striking range as President Donald Trump and his national security aides mulled the scope and timing of an expected military assault.

Trump's U.N. ambassador, Nikki Haley, said the president had not yet made a final decision, two days after he tweeted that Russia should "get ready" because a missile attack "will be coming" at Moscow's chief Middle East ally. The presence of Russian troops and air defenses in Syria were among numerous complications weighing on Trump, who must also consider the dangers to roughly 2,000 American troops in the country if Russia were to retaliate for U.S. strikes.

Despite strong reservations expressed by some Democrats in Congress, the likelihood of Trump ordering a military strike aimed at degrading Syria's chemical weapons capacity seemed high given his public threats and indications from Britain and France that they, too, believe the Syrian government was behind the April 7 poison gas attack and must be penalized.

The Organization for the Prohibition of Chemical Weapons, based in the Netherlands, announced it would send a fact-finding team to the site of the attack at Douma, near Damascus. U.N. Secretary-General Antonio Guterres said Friday the first team was already in Syria and a second was expected soon. It was not clear whether the presence of the investigators could affect the timing of any U.S. military action.

At the White House, spokeswoman Sarah Huckabee Sanders said U.S. officials at various levels were still consulting with allied officials. She said the White House is confident that Syria was responsible for the deaths at Douma. "We also hold Russia responsible for their failure to stop chemical weapons attacks from taking place," she said.

Three Democrats in the Senate, led by Jack Reed of Rhode Island, the ranking member of the Armed Services Committee, sent a letter to Trump urging him to make a public and compelling legal case for any attack.

"This issue is of critical importance and the American people should be fully informed about your rationale for deploying American military power and the objectives of any U.S. military action in Syria," Reed wrote, joined by Sens. Dick Durbin of Illinois and Bob Menendez of New Jersey. "As previous commanders in chief have done in similar situations, we believe you should present a clear public articulation of these matters to the American people at the earliest appropriate time."

The British Cabinet gave Prime Minister Theresa May the green light to join the U.S. and France in planning military strikes in Syria. She and French President Emmanuel Macron spoke separately with Trump on Thursday. Macron, who spoke to Trump again on Friday, said France had proof the Syrian government launched chlorine gas attacks and his country would not tolerate it.

In Moscow, the Defense Ministry accused Britain of staging a fake chemical attack in Douma, a Syrian town outside Damascus. The incident a week ago, believed to have killed dozens of civilians, is the focus of international outrage and is the basis for Trump's threat to unleash a missile barrage to punish the government of President Bashar Assad.

Britain called the Russian charge a "blatant lie." Tensions between Moscow and London have escalated since the recent poisoning of a former Russian spy in Salisbury, England. Britain accused Moscow of ordering the poisoning; Moscow denies it.

The Kremlin said Russian President Vladimir Putin spoke with Macron and the two leaders agreed to coordinate their actions to avoid further military escalation in Syria. It was unclear how this might influence the direction of events.

Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said images of victims of the purported attack were staged with "Britain's direct involvement." He provided no evidence.

As Trump deliberated, the Navy said the USS Winston S. Churchill, a destroyer armed with Tomahawk cruise missiles, was approaching the Mediterranean. It is joining the USS Donald Cook within range of Syria for potentially firing Tomahawks, which were the weapon of choice when the U.S. struck Syria in April 2017 to punish it for using chemical weapons. Navy submarines also are capable of firing Tomahawks; their movements are secret but they commonly operate in the Mediterranean.

Defense Secretary Jim Mattis was not seen publicly Friday, but he is known to argue for ensuring that military action in any context is linked to a broader political strategy. It's unclear what policy the Trump administration is pursuing in Syria beyond fighting the Islamic State militants and hoping for a U.N.-brokered end to the civil war. In congressional testimony on Thursday, Mattis cited the risk of military action in Syria "escalating out of control."

A Washington think tank, the Institute for the Study of War, said Friday that Syrian and Russian warplanes had relocated to heavily defended commercial airfields across Syria, including in Latakia province on the Mediterranean coast. An institute Syria specialist, Jennifer Caferella, wrote in an analysis Friday that Trump appeared likely to authorize strikes against Syrian military targets soon, perhaps targeting Assad's remaining air forces and chemical weapons production facilities.

"A new round of strikes will most likely impose costs and degrade the regime's capability to launch such (chemical weapons) attacks by damaging Assad's remaining air force," she wrote.

Haley, the U.S. ambassador to the U.N., told an emergency meeting of the Security Council that should the United States and its allies decide to act in Syria, it would be to defend "a bedrock international norm that benefits all nations" - the prohibition of the use of chemical weapons.

She said Friday that "the United States estimates that Assad has used chemical weapons in the Syrian war at least 50 times."

___

AP writers Jill Colvin and Edie Lederer contributed.

Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.