At first, the differences between the United Arab Emirates two leading cities were merely cultural. Abu Dhabi built world-class museums as fast as Dubai put up extravagant shopping malls _ one with a ski slope inside.

But the healthy competition that has helped transform them into two of the Middle East’s most vibrant and bustling cities has soured as the tiny emirates grow increasingly divided over their relations with two other rivals _ Iran and the United States.

Dubai’s skyscrapers, American-style theme parks and sprawling beaches clashed with the more prim sophistication of Abu Dhabi, which is building a symphony orchestra and branches of the Guggenheim and Louvre museums.