Commuters continue to face inconvenience on Metro B1 line.

Rome's Metro B1 was out of action again for several hours on Friday, due to lack of available trains, in the latest disruption to the troubled subway line in recent days.

The city's public transport provider ATAC apologised for the inconvenience, saying that the B1 line linking the Bologna and Jonio stops was closed in both directions and that substitute buses had been activated.

The service reopened at lunchtime but not before ATAC came under a hail of criticism on social media from commuters tired of delays and unscheduled closures.

• Rome's Metro A to close early for 18 months

The disruption comes as capital prepares to carry out "important maintenance and safety works" on both Metro A and B which will result in prolonged early closures on both lines.

Metro B is to close at 21.00 every night from 19 April to 6 June, while Metro A line will close at the same early time, for about 18 months, from 15 June.

For the duration of the works the A line is expected to stay open at weekends until the usual hour of 01.30.

Rome's underground recently made international news after the city decorated a Metro A train in the colours of the Ukraine flag, with the words for 'peace' in Italian and Ukrainian.

Photo La Repubblica