Monitors say Kurdish-led Syrian forces, backed by a U.S.-led air coalition, are battling Islamic State extremists on the northern outskirts of Raqqa, the IS de facto capital seized by the militant group three years ago.
The activist Syrian Observatory for Human Rights said Saturday that the U.S.-backed Syrian Democratic Forces (SDF) advanced within four kilometers of Raqqa as fighting raged at several points north and east of the besieged city.
An SDF spokesman, speaking Friday, said an anti-jihadist assault on the fortified northern city would most likely begin in the next several months.
The loosely knit anti-jihadist coalition pushing to liberate Raqqa includes SDF forces attacking from the north and rival Syrian ground forces backed by Shi'ite allies and Russia pressing toward the city from the south.
Sunni Arab and Turkmen militias are also involved, along with a separate contingent of Turkish-backed forces opposed to a faction of Kurdish fighters in the U.S.-backed SDF alliance.
Conflicts within the widely divergent anti-jihadist alliance have so far been addressed with quiet diplomacy by U.S., Turkish and Russian military commanders.
As the disparate anti-jihadist forces gather near Raqqa — motivated largely by the single objective of destroying Islamic State — U.S. advisers have sought to keep peace within the factions by creating buffer zones separating Kurdish fighters from Turkish-backed forces.
It remains unclear what role, if any, Syrian government forces and their Russian allies will play in the planning or execution of the complex offensive.
Anti-jihadist push gains steam
The push to retake Raqqa appears to have gathered strength since U.S. President Donald Trump announced a decision Wednesday to arm Kurdish-led forces with heavy weapons.
That decision has been roundly criticized by Turkey, which sees a key Syrian Kurdish unit in the SDF alliance, the YPG, as an extension of the outlawed Kurdistan Workers' Party (PKK).
Turkish leaders have voiced fears that any heavy weaponry used by the SDF against extremists at Raqqa will eventually fall into the hands of PKK fighters, who have battled the Turkish government for an autonomous region in Turkey's southeast for more than three decades.
On Wednesday, Erdogan, who opens an official visit to Washington on Tuesday, told reporters that he hoped "this [U.S.] mistake will be reversed immediately."