Stock markets in the Gulf closed down on Thursday, as fears of a possible U.S. military action against Iran raised concerns that the region would bear the brunt of any Iranian retaliation. The deployment of a U.S. aircraft carrier and supporting warships to the Middle East this week has broadened U.S. President Donald Trump's options for potential military action, following his repeated threats to intervene over Iran's crackdown. In mid-January, Saudi Arabia, Qatar, Oman and Egypt urged Washington not to carry out a strike on Iran. The UAE said on Monday it would not allow its airspace, territory, or waters to be used for hostile military action against Iran, reaffirming its neutrality and commitment to regional stability. The Qatari index <.QSI> finished 0.6% lower, with Qatar National Bank <QNBK.QA>, the Gulf's biggest lender by assets, sliding 1.3%.