ANKARA - Turkey said on Thursday Washington's denial that it intended to build a border force in Syria was "important," but added Ankara would not remain silent in the face of any force that threatened its borders.Turkey reacted angrily after the US-led coalition said it would help its Syrian militia allies, dominated by the Kurdish YPG, to set up a new 30,000-strong border force.US Secretary of State Rex Tillerson said on Wednesday he had met Turkey's foreign minister to clarify the issue and said the situation had been "misportrayed, misdescribed. Some people misspoke.""This statement is important but Turkey cannot remain silent in the face of any formation which will threaten its borders," Turkish Justice Minister Abdulhamit Gul told broadcaster NTV when asked about Tillerson's comments.Ankara views the YPG as an extension of the Kurdistan Workers Party (PKK) militant group, which has fought an insurgency in southeast Turkey since 1984. Turkey, the United States and the European Union deem the PKK a terrorist group.Turkey and the United States, both allies in NATO, have been on the same side for much of Syria's civil war, both supporting rebels fighting to overthrow Syrian President Bashar Assad. But a decision by Washington to back Kurdish forces fighting against Islamic State infuriated Ankara.