Qatar and UAE exchange office in Doha, Qatar, June 13, 2017.

Qatar's peg with the U.S. dollar is a potential headache – and a potent economic weapon. The emirate's fixed currency has supported financial stability in a small country that overwhelmingly depends on energy exports. Tensions with Gulf neighbours may make fears of a devaluation of the riyal self-fulfilling. But breaking the peg could also turn the tables on Qatar's enemies in the region.

Pressure has built up on the currency since an alliance led by Saudi Arabia and the United Arab Emirates imposed an economic blockade two weeks ago. They want Doha to sever ties with Iran and militant groups such as the Muslim Brotherhood, as well as shutting down its troublesome Al Jazeera news network. Food imports have been blocked and some exports disrupted. Qataris have been ordered to leave neighbouring states.