Doctors Without Borders said Sunday that fighting between Iraqi forces and Kurdish fighters near the border threatens the delivery of humanitarian aid to half a million newly displaced civilians in northeastern Syria.
The medical charity, also known as MSF, said it is "extremely concerned" because the fighting threatens its only cross-border supply routes between the two countries.
Scattered clashes have erupted in recent weeks as Iraqi forces have retaken disputed territory from the Kurds, part of a crisis sparked by last month's Kurdish vote for independence. Federal forces have sought to regain control of the country's borders from forces loyal to the Kurdish regional government.
The Fishkhabur crossing is the only gateway for residents, aid workers and journalists to enter northeastern Syria. A nearby crossing, used for commercial traffic, was closed on Thursday due to fighting in Iraq, and has yet to reopen.
U.S. officials say the fighting has also hindered the movement of military equipment and supplies in Syria and Iraq, where Iraqi, Kurdish and other allied forces are battling the Islamic State group.
A Kurdish official on the Syrian side of the border said access for aid workers and journalists has not been affected. The official spoke on condition of anonymity because he was not authorized to brief reporters.
"It is already very complicated trying to provide aid in North-East Syria where large parts of cities have been destroyed by fighting and airstrikes and nearly 500,000 people have been displaced and are living under poor conditions," MSF said in a statement.
"If the border between Syria and Iraq closes for humanitarian aid, the millions of already vulnerable people will no longer have access to critical medical care."