In a phone conversation on Thursday with Turkish Defense Minister Hulusi Akar, Esper noted that Washington opposes Ankara's military operations in Syria as they risk the "progress made by the Defeat-ISIS Coalition", according to the statement, Xinhua reported.
Esper also noted that Turkish offensive risks serious consequences for Turkey, but the Pentagon chief did not elaborate.
"Secretary Esper strongly encouraged Turkey to discontinue actions in northeastern Syria in order to increase the possibility that the United States, Turkey and our partners could find a common way to de-escalate the situation before it becomes irreparable," the statement said.
US President Donald Trump said on Thursday that he hopes to mediate between Turkey and the Syrian Kurds, and also threatened to punish Turkey if its offensive in northeast Syria goes beyond limits.
A senior state department official reaffirmed Trump's warning to Turkey in a teleconference briefing later in the day, saying that the US is willing to impose significant costs if "Turkey acts in a way that is disproportionate, inhumane, or otherwise goes beyond the lines that the President has in his own mind".
US lawmakers from both parties had announced a framework for sanctions against Turkey, which includes sanctions on senior Turkish government officials and prohibition of all US military business and transactions with Turkey, among others.
Turkish Foreign Minister Mevlut Cavusoglu responded on Thursday that Turkey would retaliate if the US imposed sanctions over its offensive into northeast Syria, according to media reports.
Turkey regards the Kurdish-led Syrian Democratic Forces (SDF) as an extension of Turkey's Kurdistan Workers' Party, which is listed as a terrorist organization by Turkey, while the US considers the SDF an ally in the fight against the Islamic State.
( With inputs from IANS )