US President Donald Trump’s national security adviser said Sunday during a visit to Israel that the American military withdrawal from Syria must be done with the defense of allies “assured.”

“We’re going to be discussing the president’s decision to withdraw, but to do so from northeast Syria in a way that makes sure that ISIS is defeated and is not able to revive itself and become a threat again,” John Bolton said when meeting Israeli Prime Minister Benjamin Netanyahu in Jerusalem.

“And to make sure that the defense of Israel and our other friends in the region is absolutely assured, and to take care of those who have fought with us against ISIS and other terrorist groups.”

Trump’s announcement on December 19 that the US would immediately withdraw its troops from Syria alarmed America’s allies, and he has since spoken of “slowly” pulling troops out “over a period of time.”

The Israelis are particularly worried about the move because they believe it could allow the Jewish state’s main enemy Iran to expand its presence in the neighboring country.

Bolton told journalists traveling with him earlier in the day that conditions such as guarantees on the safety of America’s Kurdish allies must be met before troops are withdrawn, NBC News reported.

Bolton also said all 2,000 US forces may not be withdrawn, according to the report.

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.

– with reporting by Agence France-Presse