The United States has largely avoided wading directly into the Syrian conflict or confronting President Bashar Al Assad and his allies throughout the seven-year war.
In the early years of the conflict, which erupted in early 2011, Washington was part of a regional and western coalition that backed and armed vetted opposition groups who were fighting to topple the Assad regime. The limited armaments left the rebel fighters always at a disadvantage, while radical groups found their way to Syria, including militants from ISIS.
As ISIS captured a wide swath of Iraq and Syria in 2014, the US began conducting air strikes against the group and shifted its Syria policy to fighting the militants. The US sent advisers into Syria and backed local allies, who captured territories as ISIS collapsed.
But as the conflict got more complex — Russia launched its air campaign in Syria in September 2015 and Turkey a few days before — the US found itself increasingly caught up in frictions with other regional players, and at times acted against threats or the repeated use of chemical weapons against civilians.
Here's a look at significant times when US forces used air and missile strikes to expand their role in Syria beyond the fight against ISIS:
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April 13, 2018: President Donald Trump announces the United States, France and Britain have launched military strikes in Syria to punish President Bashar Al Assad for a suspected chemical attack against civilians and to deter him from doing it again. Mr Trump says the US is prepared to exert sustained pressure on Mr Assad.
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February 7, 2018: The US military launches rare air strikes and artillery rounds against Syrian government-backed troops after as many as 500 attackers started what appeared to be a co-ordinated attack on US-backed Syrian forces and US advisers in eastern Deir Ezzor province. US officials said the strikes were in self-defence after pro-government forces began firing artillery and tank rounds at the US-backed Syrian Democratic Forces. About 100 of the attackers were killed, the official said. Russian officials said a number of Russian contractors were killed in the US strike.
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June 18, 2017: US warplanes down a Syrian air force jet, the first such incident. The downing of the Syrian SU-22 came after it bombed US-allied forces fighting ISIS militants west of Raqqa city. A number of US-allied fighters were injured. US officials said they acted to defend allies attacked by the Syrian government as both rival forces raced toward Raqqa city, at the time the de facto capital of the ISIS militants.
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June 8, 2017: US officials say US jets downed an armed Iranian-supported drone that had fired on US troops in southern Syria near a base where the international coalition against ISIS militants is training Syrian rebel forces. The weapon fired by the drone didn't detonate. US officials called the drone a direct threat to the coalition, and it came hours after an earlier attack by pro-government forces in the same area against the US-backed forces in the camp.
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June 6, 2017: US air strikes strike pro-Syrian government forces who approached a camp in southern Syria where US-backed Syrian forces and US advisers were training as part of the anti-ISIS effort. It was the second such confrontation between US forces and pro-Syrian government forces in less than three weeks. US.officials described the forces as Iranian-backed and said they had approached and attacked the base where US-backed forces were training near the border with Jordan. US officials said air strikes destroyed two artillery pieces and an anti-aircraft weapon and damaged a tank in the attack.
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May 18, 2017: A US air strike hits pro-Syrian government forces that the coalition said posed a threat to American troops and allied rebels operating near the border with Jordan in southern Syria. It was the first such close confrontation between US forces and fighters backing Mr Assad. US officials said the American air strike hit pro-Syrian government forces as they were setting up fighting positions in a protected area near Tanf and the border with Jordan. They said a tank and a bulldozer were also hit.
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April 6, 2017: In retaliation for a government chemical weapons attack in northern Syria that killed nearly 90 people, including 31 children, the US fires 59 Tomahawk missiles overnight at the government-controlled Shayrat airbase in central Syria. US officials said the Syrian military planes that dropped the chemicals had taken off from there, and claimed all but one of the missiles struck their targets, hitting multiple aircraft and air shelters, and destroying the fuel area.
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September 17, 2016: A mistaken coalition air assault reportedly killed more than 90 Syrian government troops in Deir Ezzor. The US military said it was human error and an honest mistake, as it was targeting what were believed to be ISIS positions.
