Dubai (CNN Business) The CEO of Siemens says the United Kingdom must provide clarity on trade or risk further declines in investment.

Siemens SIEGY "Nobody puts money [into] uncertainty. That's not the way it works,"boss Joe Kaeser told CNN Business' Emerging Markets Editor John Defterios on Monday.

The United Kingdom is scheduled to leave the European Union on March 29, but there's still no exit agreement in place.

Business lobby groups are still clamoring for clarity on the terms of the divorce and Britain's future trading relationship with the European Union.

"The biggest challenge today for everybody ... is the uncertainty," said Kaeser.

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