BEIRUT — With the Trump administration's decision to supply Syria's Kurdish fighters with heavier weapons, U.S. troops inside Syria are in the crossfire between Turkey, a powerful NATO ally, and the Kurdish fighters that Ankara deems as terrorists.
In only a few months under President Trump, the U.S. has almost doubled the number of troops in northern Syria, taking a highly visible role that also risks a backlash from militants such as the Islamic State group and the Iranian-backed Hezbollah, and even pro-Turkey Syrian fighters angered by the U.S. move to arm the Kurds.
Tuesday's decision to arm the Kurds is a public rebuff to Turkey's President Recep Tayyip Erdogan a week before he meets Trump in Washington. For months, Erdogan has been trying to convince the U.S. to cut off its support for the Kurds and partner instead with Turkey-backed fighters to liberate the Islamic State group stronghold of Raqqa.
The dispute could ignite more fighting between Turkey and the Kurds as they gear up for a major operation to retake the city, with U.S. troops smack in the middle.
The growing U.S. involvement in Syria's civil war stands in sharp contrast to the caution adopted by former President Barack Obama and has alarmed officials in Damascus and its backers in Tehran.
Last month, Trump gave orders to fire 59 Tomahawk missiles at an air base in central Syria in response to a devastating chemical weapons attack blamed on Syrian President Bashar Assad's forces. It was the first time the U.S. has attacked Syrian forces in the six-year civil war.
Although U.S. officials have said repeatedly since then that the war against the Islamic State group in Syria remains the priority, that strike — coupled with the buildup of forces in the north — has raised speculation of longer term U.S. ambitions in Syria and concerns about a more permanent project.
Under Trump, the Pentagon has made quiet, incremental additions to troop levels in Syria, adding hundreds of Marines to provide artillery support and sending more advisers to work with Kurdish units ahead of the fight for Raqqa. The official limit on U.S. troops has remained at 503 since shortly before Obama left office, but U.S. commanders this year have added hundreds of troops, including a Marine artillery unit, on what they call a temporary basis, raising the total to about 900.
These have taken on a more visible role, often aimed at keeping Turkey and the Kurds from battling each other and focused instead on the fight against IS.
On April 30, U.S. forces accompanied by Kurdish People's Protection Units (YPG) began patrols along the Turkey-Syria border, acting as a buffer after Turkish airstrikes in the area killed 20 Kurdish fighters. The spokesman for the U.S.-led coalition against IS, Col. John Dorrian, said U.S. troops were about 6 miles from the strikes and put American forces at risk.
Images of U.S. troops in armored personnel carriers with American flags and maneuvering down rural roads in northern Syria spread quickly on social media, triggering alarm in a region where there are political sensitivities about the footprint of U.S. troops and fears about occupation forces.
In a crowded battlefield like Syria, the growing U.S. presence brings with it a greater risk of confrontation with competing players.
U.S. special operations forces are embedded with the Kurdish-led fighters known as the Syrian Democratic Forces as they prepare for battle around Raqqa.
"There is a concern that American forces in Syria can be targeted because there are many who are not happy about their presence," said Mutlu Civiroglu, a Washington-based Kurdish affairs analyst. "Although American forces are well-protected by the Kurds, still such possibly always exists."
Earlier this month, Islamic State group militants staged a surprise attack at a crossing frequently used by Iraqi and Syrian civilians seeking safety in northeastern Syria, killing nearly 40 people, mostly civilians.
The IS-linked Aamaq news agency said militants struck four YPG positions in Hasakeh province in northeastern Syria. Ominously, it added that two of the targeted locations were "suspected of hosting U.S. troops."
Also concerned about the growing U.S. presence is northern Syria is Iran, which has bankrolled the presence of thousands of Shiite militiamen in Syria to bolster Assad's military and seeks to secure a land route from Beirut to Tehran that goes through Damascus and Baghdad. Iran views the prospect of permanent U.S. bases in Syria with a high degree of unease, reflected most recently by comments by officials of the Iranian-backed Lebanese Hezbollah group.
Earlier this month, Sheikh Ali Daamoush, a senior Hezbollah official, warned the U.S. against "trying to regain a presence in the region" via direct intervention in Syria and Iraq, and setting up bases there.
He said the "Axis of Resistance" — a reference to an alliance of Iran, Syria and Hezbollah — "will not allow Syria to fall in the hands of America and Israel."
Although there is no immediate danger in the U.S. presence and the alliances that Washington has formed there, Iran and Syria are concerned about the growing American sphere of influence and what it could mean for Iranian dominance in Syria and Iraq in the long term, according to Hassan Hassan, a Syria expert.
"That is why we are seeing more pro-Iranian militias being built in or for northern and eastern Syria in recent months," he added.
"For now, things look tolerable for Iran, but it is not clear what the U.S. could do with their buildup in that region. It can go different ways, depending on the U.S. thinking down the road."
Associated Press writer Sarah El Deeb in Beirut contributed.