The Pentagon said on Monday Turkey's Afrin offensive caused an "operational pause" in their operations against Islamic State (IS).

"The U.S. is expected to step in to stop YPG/PYD forces shifting -- under U.S. control -- from Manbij to Afrin," Turkish presidential spokesman Ibrahim Kalin said in televised remarks, AFP reported.

"This is our most natural right. Whether they do it or not is a separate question but we have taken all the necessary measures on the ground," he said.

The Turkish army on January 20 launched an operation against the Kurdish forces in their enclave of Afrin near the border.

Washington has voiced concerns about the safety of U.S. troops in Manbij amid Turkey’s operation in northeastern Syria. There are about 2,000 American soldiers currently stationed in Manbij.

Meanwhile State Department’s Spokeswoman, Heather Nauert said the U.S. is concerned over the Turkish operation on Afrin due to “an escalation of violence,” adding that Washington has called for a de-escalation of violence in the region.

“The more that we would see Turkish forces enter into Syria proper, deeper into Syria, the more that it stands to create a potential humanitarian crisis,” she said on Tuesday, March 6.

Reporter’s code: 50101