Gulf equity indexes mostly fell on Tuesday as tension flared between regional oil powers and neighbours Saudi Arabia and the United Arab Emirates.

Dubai's main share index .DFMGI was down around 2%, LSEG data showed, while Abu Dhabi's main index .FTFADGI dropped 0.9% and Saudi Arabia .TASI was down 0.6%.

Saudi Arabia said its national security was a red line, hours after a Saudi-led coalition launched strikes on what it described as foreign military support to UAE-backed southern separatists in Yemen, and also asked UAE forces to leave the country.

An offensive this month has pitted the Southern Transitional Council (STC) against Saudi-supported Yemeni government troops, bringing the two Gulf allies closer than ever to an all-out conflict in Yemen, mired in civil war since 2014.

The Dubai index was on course for its biggest daily decline since June. Blue-chip developer Emaar Properties EMAR.DU fell 3.5% and top lender Emirates NBD ENBD.DU was 1.7% lower.

Among Saudi shares, Al Rajhi Bank 1120.SE eased 0.7% and Saudi National Bank 1180.SE, the country's biggest lender by assets, retreated 1.1%. Oil giant Saudi Aramco 2222.SE was down 0.3%.

Oil prices - a catalyst for the Gulf's financial markets - were little changed after Russia accused Ukraine of attacking President Vladimir Putin's residence and investors sought clarity on Ukraine peace talks to gauge potential supply disruptions.

The Qatari index .QSI was down 0.4%, with Qatar National Bank QNBK.QA, the Gulf's biggest lender, dropping 0.7%.

Bahrain .BAX bucked the trend with a 0.4% rise after the country announced several fiscal reform measures on Monday.

(Reporting by Ateeq Shariff in Bengaluru and Federico Maccioni in Dubai; Editing by Kirsten Donovan)