Kuwait will join the emerging market index in two phases, on Sept. 24 and Dec. 24. Arqaam Capital estimates the inflows in the two phases combined at $1 billion.

Kuwait's main index was down by 0.8 percent as National Bank of Kuwait (NBK) fell 1.5 percent and logistics company Agility dropped 1.9 percent.

The index has gained almost 11 percent so far this year. This quarter alone it has surged 8 percent on expectations of inflows in anticipation of the FTSE Russell inclusion.

Elsewhere, Gulf markets were largely positive, with Qatar's index adding 0.6 percent and Dubai's benchmark up 0.4 percent. The Abu Dhabi index rose 0.3 percent.

In Qatar, the region's biggest lender, Qatar National Bank (QNB), rose 1.4 percent, while Qatar Islamic Bank climbed 1.3 percent.

Dubai's index was supported by blue-chip developer Emaar Properties, up 1.3 percent, and logistics company Aramex, which gained 2.4 percent.

In Abu Dhabi, Abu Dhabi Commercial Bank (ADCB) and Union National Bank (UNB) rose 1.6 percent and 1 percent, respectively. ADCB and UNB are in merger talks along with unlisted Al Hilal Bank.

Saudi Arabia's stock market is closed for the country's national day.