ISTANBUL — President Recep Tayyip Erdogan rejected a U.S. offer to mediate a cease-fire between Turkish forces and Kurdish militants in northeastern Syria and demanded Wednesday that the Kurds “drop their weapons” as the quickest way to halt the fighting.

The Turkish leader ordered Kurdish fighters to disarm and withdraw from designated border areas before nightfall Wednesday. Erdogan launched the offensive targeting Syrian Kurdish militants in northeastern Syria last week.

"The terrorists should drop their weapons and leave the area that we have identified as the safe zone," he said in a speech Wednesday to the Turkish parliament. He vowed to press forward with the campaign to rout Kurdish-led fighters, known as the Syrian Democratic Forces, or SDF, from a wide swath of territory along the border.

"Nobody can stop us until we reach 30 to 35 kilometers" (19 to 22 miles) inside Syria, he said.

Vice President Mike Pence and Secretary of State Mike Pompeo were scheduled to travel Wednesday to Turkey as part of the administration's efforts to quell the chaos unleashed by the Turkish offensive, which critics warned could lead to a security vacuum in northeastern Syria.

The United States partnered with the SDF to battle the Islamic State in Syria. As the Turkish operation began, however, President Donald Trump ordered the withdrawal of U.S. troops from the area.

Erdogan said Wednesday that the U.S. delegation "must be prepared" to consider Turkey's concerns in northeastern Syria, where a Kurdish-led administration has governed for years.

Turkey views the SDF as terrorists for its links to the Kurdistan Workers' Party, or PKK, which has waged a decades-long struggle for Kurdish autonomy inside Turkey.

Erdogan told reporters late Tuesday that Turkey would "never declare a cease-fire" and that he was unconcerned with U.S. sanctions targeting senior Turkish officials over the offensive.

"They are pressuring us to stop the operation. They are announcing sanctions. Our goal is clear," he said of the United States and other Western nations, in remarks carried by the state-owned Anadolu news agency.

He said he refused a U.S. proposal to broker a truce with Syrian Kurdish militants.

Turkey will not "sit down at the table with terror groups," Erdogan said, Anadolu reported.

The Turkish offensive and U.S. move to withdraw troops prompted Syrian Kurdish leaders to strike a surprise deal with the government of Syrian President Bashar Assad earlier this week, paving the way for pro-government forces and allied Russian troops to fill a security vacuum in the north.

Russia announced Tuesday that its units were patrolling between Turkish and Syrian military forces near the strategically important Syrian town of Manbij to prevent a confrontation. U.S. troops had withdrawn from Manbij just hours before.

Kremlin spokesman Dmitry Peskov said Wednesday that Moscow expected the Turkish operation "to be proportionate to the goal of national security."

He did not say when Russia believes Turkey might conclude the offensive.

The Washington Post’s Kareem Fahim in Istanbul, Sarah Dadouch in Beirut and Natasha Abbakumova in Moscow contributed to this report.