Hague also urged tourists to follow travel advice after army chief General Prayut Chan-O-Cha announced the putsch on live TV, following months of political unrest.
"I am extremely concerned by today's coup," Hague said in a statement.
"The UK urges the restoration of a civilian government that has been democratically elected, serves the interests of its people and fulfils its human rights obligations."
Hague said Thai authorities should set out a "quick clear timetable for elections to help re-establish the democratic framework of governance."
The Foreign Office earlier said it urged "all sides to put aside their differences".
Hague's statement echoed that of the European Union, which called for a "rapid" return to democracy, but did not go as far as French President Francois Hollande's condemnation.
The Pentagon said it was reviewing US military cooperation with Thailand after the coup.