"It will be in the next 24 hours, I can only tell you it will be very soon," said the top official, who asked for anonymity while commenting to a small group of journalists on Tuesday, Efe news reported.
The source refused to say whether Pence will meet with Turkish President Recep Tayyip Erdogan, remarking only that the aim of the trip is to negotiate a cease-fire and show the Turkish government that the US "is bothered" by its offensive into the neighbouring country.
The official said that President Donald Trump spoke by telephone on Monday with Erdogan and with the commander of the Syrian democratic forces (SDF), Mazlum Abdi, whose organization is the main armed alliance headed by the Syrian Kurds, to transmit to them his intention of achieving a cease-fire.
"And by ceasefire what I mean is forces on the ground stop moving on the ground. Certainly Turkish forces and I think we could probably speak for the SDF," the official said.
When asked about the date on which Washington would like the cease-fire to begin, the official refused to answer, saying only: "We'll see what happens with the Turks and if they want a cease-fire. They are already addressing the sanctions and, as you know, we have meetings in Ankara in the very near future."
On Monday, the US government imposed sanctions on three Turkish government ministers and announced that it will increase tariffs on Turkish steel to 50 percent, at the same time that it closed the door to a bilateral trade agreement.
The situation on the ground has changed considerably in 5recent hours with forces loyal to the Syrian government of Bashar al Assad, backed by Moscow, having occupied a large part of northern Syria, while the US-led international coalition has been withdrawing from that area.
According to the official, Washington and Moscow came to an agreement on the withdrawal of the coalition forces, and last Sunday the US announced it would withdraw its entire force of about 1,000 troops from northeastern Syria.
Some US media outlets, including The Washington Post, have reported the presence of Russian troops in northern Syria.
The State Department official confirmed that information, although they said that the Russian presence is small and that there are less than 100 Russian troops in the area.
"There are no more than a few Russ and a big Russian flag to attract attention," the source said.
The Turkish offensive, which was launched on October 9, is directed at the US-allied Syrian Kurdish militias, the main body of fighters making up the Syrian democratic forces. The Kurds have been allies of the US in fighting the Islamic State, although Turkey considers the former to be terrorists.
( With inputs from IANS )