Spain is considering constitutional changes that could allow its regions to hold referendums on independence in the future, the foreign minister says.

Alfonso Dastis has told the BBC a nationwide vote on the issue could be held.

The move is in recognition of the events in Catalonia, where the regional government was deposed after a unilateral declaration of independence.

Protests were held against the detention of the region's ex-leaders.

Meanwhile, Spain's constitutional court has ruled that the declaration of independence was "unconstitutional and void".