"This is a cause-and-effect mission", Bolton said, adding, "Timetables or the timing of the withdrawal occurs as a result of the fulfillment of the conditions and the establishment of the circumstances that we want to see".
Ahead of his departure for the Middle East on Saturday, Bolton warned that the USA withdrawal from Syria should not be seen as an invitation for Syrian leader Bashar al-Assad to use chemical weapons.
US President Donald Trump's decision last month to leave Syria has exposed the Kurdish group to possible Turkish attacks.
He said the withdrawal would take place in northeastern Syria, while some forces could remain to the south at the al-Tanf garrison as part of efforts to counter Iran's presence.
This, he said, was to make sure that Turkey meets Trump's key condition to follow up on his withdrawal plan.
The Britain-based Syrian Observatory for Human Rights, a group that monitors the Syrian civil war, said in a report Sunday that the IS attack occurred the previous day in the village of Shaafa in eastern Deir el-Zour province amid fierce clashes between the Kurdish-led Syrian Democratic Forces, backed by the USA -led coalition, and IS militants.
Assad has denied the use of chemical attacks, blaming rebels in Syria for staging chemical attacks as to provoke a response from the US-led coalition, while Russian Federation said it had proof that the alleged chemical weapons attack in Syria's Eastern Ghouta was staged on orders from London.More news: Netflix Warns Against People Doing 'Bird Box Challenge'
Two British special forces soldiers were seriously injured after a missile attack by the Islamic State terror group in Eastern Syria on Saturday amid fierce fighting in the region.
Despite backing from the US-led coalition and success in pushing back IS, Kurdish-led forces have at times incurred heavy losses.
For his part, Bolton said the United States backed Israel's right to self-defence and said the Trump administration will continue to work with Israel to counter "the continuing threat of Iran's quest for deliverable nuclear weapons".
Bolton's visit was part of a United States effort to reassure allies after Trump's announcement.
Secretary of State Mike Pompeo is following Bolton to the Mideast this coming week for an eight-country tour of Arab allies to shore up support for the administration's partners in the region.
"And why it's important that all countries recognise Israel's sovereignty over the Golan Heights".
Israel annexed east Jerusalem after capturing it from Jordan in the 1967 war, a move not recognized by most of the global community. "I've discussed this with the president, and I hope I have a chance to to show it to you directly tomorrow on our visit".
"I think they know who their friends are", he said.