Donald Trump has said the US “will retaliate” after three Americans were killed in a suspected Islamic State attack in Syria.

Two US service members and one civilian died and three other people were injured in an ambush on Saturday by a lone IS – also often called ISIS in Syria and Iraq – gunman, according to the he US military’s Central Command.

The attack on US troops in Syria is the first to inflict fatalities since the fall of President Bashar Assad a year ago.

“This is an ISIS attack,” the US president told reporters at the White House before leaving for the Army-Navy football game in Baltimore.

He paid condolences to the three people killed and said the three others who were wounded “seem to be doing pretty well”.

In a post on his Truth Social platform, Mr Trump said “there will be very serious retaliation”.

The shooting took place near historic Palmyra, according to the state-run SANA news agency, and the casualties were taken by helicopter to the al Tanf garrison near the border with Iraq and Jordan.

The UK-based Syrian Observatory for Human Rights said the attacker was a member of the Syrian security force.

Syria’s Interior Ministry spokesman Nour al Din al Baba said authorities are looking into whether the gunman was an IS member or only carried its extreme ideology, and denied reports suggesting he was a security member.

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Central Command earlier said in a post on X that the gunman was killed, while the identities of the service members killed wouldn’t be released until 24 hours after their next of kin have been notified.

Pentagon chief spokesman Sean Parnell said the civilian killed in the attack was a US interpreter.

US defence secretary Pete Hegseth posted on X: “Let it be known, if you target Americans – anywhere in the world – you will spend the rest of your brief, anxious life knowing the United States will hunt you, find you, and ruthlessly kill you.”

The US has hundreds of troops deployed in eastern Syria as part of a coalition fighting IS.

The group was defeated on the battlefield in Syria in 2019 but the UN says the group still has between 5,000 and 7,000 fighters in Syria and Iraq, and its sleeper cells still carry out deadly attacks.

Syria’s interim president, Ahmad al Sharaa, made a historic visit to Washington DC last month as Syria signed a political cooperation agreement with the US-led coalition against IS.

“This was an ISIS attack against the US, and Syria, in a very dangerous part of Syria, that is not fully controlled by them,” Mr Trump said in his social media post, adding that Mr al Sharaa was “extremely angry and disturbed”.

National Guard troops went door-to-door on Friday to evacuate a farming city north of Seattle as severe flooding in western Washington state put levees at risk.

Days of torrential rain have swelled rivers to record or near-record levels, as flooding has stranded families on rooftops, washed over bridges and ripped homes from their foundations.

Burlington, a city of nearly 10,000 residents near Puget Sound – a large inlet of the Pacific Ocean in northwestern Washington – was placed under a full evacuation order with people told to leave immediately and move to higher ground.

The Skagit River, a major waterway that flows from the Cascade Mountains through the Skagit Valley before emptying into Puget Sound, surged to a record high of nearly 38ft (11.6m) at Mount Vernon, about 10 miles south of Burlington.

“We haven’t seen flooding like this ever,” said Karina Shagren, a spokesperson for the state’s emergency management division, adding that there had been no reports of injuries or missing individuals so far.

National Guard troops and sheriff’s deputies were going door to assist with the evacuations.

Some responders were seen paddling stranded Burlington residents to safety in inflatable river rafts through the muddy floodwaters.

Later on Friday, the evacuation order was lifted for part of the city, Burlington police department spokesperson Michael Lumpkin said.

However, while water levels appeared to ease a little, Mr Lumpkin said “it’s definitely not an all-clear”.

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The intense rainfall was driven by an atmospheric river, a massive stream of moisture drawn from the ocean and carried inland over the Pacific Northwest earlier in the week.

Although rainfall has begun to ease, the National Weather Service has issued a flash-flood warning for the Skagit River basin all the way downstream to its mouth at Puget Sound.

The swollen waters could put enough strain on levees to cause them to fail, the weather service noted.

“Extensive flooding of streets, homes and farmland will be possible” if levees and dikes give way, it said.

The Burlington-Mount Vernon area in Skagit County continues to be the hardest-hit area, facing extensive flooding from days of heavy rainfall stretching from northern Oregon through western Washington and into British Columbia.

National Guard troops were also dispatched to deliver food and check on stranded residents in a number of communities cut off by flooding in adjacent Snohomish County, south of Skagit County.

The flooding washed out or forced the closure of dozens of roads throughout the region, including most of the Canadian highways leading to the port city of Vancouver in British Columbia.

Parts of northern Idaho and western Montana have also been impacted.

Donald Trump is being sued by a preservation group which wants a federal court to halt the construction of a new ballroom at the White House until it goes through multiple independent reviews and wins approval from Congress.

The National Trust for Historic Preservation’s lawsuit represents the most concrete effort so far to change or stop plans for the new $300m ballroom that would be nearly double the size of the White House before the East Wing was demolished.

“No president is legally allowed to tear down portions of the White House without any review whatsoever – not President Trump, not President [Joe] Biden, and not anyone else,” the non-profit organisation’s lawsuit states.

“And no president is legally allowed to construct a ballroom on public property without giving the public the opportunity to weigh in.”

The ballroom project has drawn criticism from preservationists, architects, and President Trump’s political opponents.

It is among several sweeping changes Mr Trump has made to the White House since he returned to office in January. He has installed gold decorations throughout the Oval Office, and paved over the lawn of the Rose Garden to create a patio similar to the setting at his Mar-a-Lago estate in Florida.

Commenting on the lawsuit, White House spokesman David Ingle said that Mr Trump is within his “full legal authority to modernise, renovate and beautify the White House – just like all of his predecessors did”.

Mr Ingle did not specify whether the president was planning to consult Congress at any point.

While nearly every president alters the White House, Mr Trump’s plans are the most extensive since President Harry Truman’s near-total renovation of its oldest section.

Unlike Mr Trump, Mr Truman obtained explicit congressional approval and funding, consulted engineering and arts authorities, and appointed a bipartisan commission to oversee the work.

Mr Trump has stressed that the project is funded with private money, including his own, but that doesn’t change how federal laws and procedures apply to a US government project.

Federal law cites “express authority of Congress” over DC projects.

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Mr Trump has long maintained that a White House ballroom is overdue, noting that large events are held in tents and guests get wet when it rains.

The lawsuit said Mr Trump never gathered public input and ignored statutes requiring consultation with the National Capital Planning Commission and the Commission of Fine Arts before tearing down the East Wing and starting work on the ballroom.