The scale of any energy price rises, and the wider impact, will depend on the magnitude of what comes next in the conflict between Israel and Iran. But it does have the potential to be "a bad shock for the global economy at a bad time" says Mohammed El-Erian, chief economic adviser at asset manager Allianz.

The U.S. dollar firmed on Monday as nervy investors sought safety, although the restrained moves suggest markets were waiting for Iran's response to U.S. attacks on its nuclear sites that have exacerbated conflict in the Middle East.