WASHINGTON — Vice President Mike Pence and Secretary of State Mike Pompeo will meet with President Recep Tayyip Erdogan of Turkey in Ankara on Thursday to relay President Trump’s demand that Mr. Erdogan negotiate a cease-fire in Syria and to reiterate the president’s threat to impose economic sanctions if he does not comply.

The president’s sending of the delegation — to also include his national security adviser, Robert C. O’Brien, and the State Department’s special envoy for Syrian affairs, James F. Jeffrey — is part of a scrambled effort to wrest back control of a chaotic situation in Syria that has endangered American forces there even as they prepared to leave.

“We want to bring our soldiers back home after so many years,” Mr. Trump said in an appearance on Tuesday in the Rose Garden. “And they’re the greatest warriors in the world.”

Mr. Trump surprised his own military when he ordered the immediate withdrawal of all 1,000 American troops in northern Syria, who had been fighting Islamic State militants alongside Syrian Kurds. The forces’ withdrawal, ahead of Turkey’s cross-border offensive, has prompted the Syrian Kurds to turn for support to the Syrian government of President Bashar al-Assad and the Russians.