The US is setting up "observation posts" along parts of the border between Turkey and Syria to help keep the focus on defeating ISIS militants in Syria, Defence Secretary Jim Mattis said on Wednesday.
The observation posts would not require additional US troops being sent to Syria, Mr Mattis told reporters. The Pentagon says it has about 2,000 troops in Syria.
The US has long complained that tensions between Turkey and the Syrian Democratic Forces (SDF), which includes the Syrian Kurdish YPG militia, have at times slowed down progress on fighting ISIS militants.
The observation posts are aimed at ensuring that Turkey and the SDF remain focused on clearing final ISIS strongholds.
"We are putting in observation posts in several locations up along the Syria border, northern Syria border, because we want to be the people who call the Turks and warn them if we see something coming out of an area that we're operating in," Mr Mattis said.
"What this is designed to do is to make sure that the people we have fighting down in the [middle Euphrates River Valley] are not drawn off that fight, that we can crush what's left of the geographic caliphate," Mr Mattis said, referring to areas controlled by ISIS.
Turkey has been infuriated with Washington's support for the YPG, which it views as an extension of the outlawed Kurdistan Workers Party (PKK) waging a decades-long insurgency on Turkish soil.
ISIS is still present in eastern Syria in a pocket east of the Euphrates River near the border with Iraq.
President Donald Trump's administration hopes that the US-backed fight against ISIS in its last foothold in north-eastern Syria will end within months but a top US diplomat recently said American forces will remain to ensure the "enduring defeat" of the militant group.
