Updated

Retirees are demonstrating across Spain, calling for higher pensions and urging authorities to ensure funding for social security.

The biggest protests are in cities including Bilbao, Barcelona and the capital, Madrid, where thousands screamed "Thieves, thieves!" at the gates of the national parliament, blocking traffic and facing off with rows of police.

Protesters held signs calling the 0.25 percent increase in pensions this year "miserable," saying it's not enough to keep up with inflation.

Organizers, including the biggest workers' unions in Spain, petitioned parliament to call on political parties to stop blocking changes to the laws on pensions.

Experts have raised concerns about the sustainability of pension payouts in an aging Spain, with fewer workers contributing to the national social security fund.