Image caption At least 24 protesters were arrested in New York City for blocking traffic and other offenses

Hundreds of US fast food workers have been arrested at protests after staging sit-ins demanding a so-called "living wage" of $15 (£9) per hour.

The protests - organised by the Service Employees International Union - took place in 150 US cities throughout the day.

Workers have been campaigning for two years to increase the current minimum wage of $7.25 an hour.

US President Barack Obama has said he supports a raise.

In New York, at least 34 protesters were arrested in Times Square outside a McDonald's restaurant. Arrests were also reported in Detroit, Chicago and Boston.

The National Restaurant Association, a trade group representing many fast-food chains, said in a statement that the protests were an attempt by unions to "boost their dwindling membership" and asked protesters to respect customers.

Two-year campaign

Since late 2012, unions and others have organised fast-food workers at restaurants like McDonald's, Burger King and Wendy's to stage walkouts and protest shareholder meetings.

Deemed the "Fight for 15" campaign, they have sought to put pressure on fast-food chains to raise the minimum wage paid to workers, as well as to provide better scheduling options to workers looking to increase their hours.

President Obama spoke out in favour of raising the minimum wage at a speech in Milwaukee, Wisconsin, on Monday.

"There is no denying the simple truth: America deserves a raise," he said.

The campaign has gathered significant support on social media, where the hashtag #strikefastfood was trending on Thursday.

However, many protests have suffered from low turnout, and on Thursday, organisers added more cities and other types of workers - including home health aides - to boost numbers.

The movement did score a victory over the summer when the National Labor Relations Board, which mediates disputes between workers and management, ruled that McDonald's, not just its franchisees, can be liable if it is found a restaurant violated labour rules, such as withholding overtime pay.

Image caption There have been some successes, as at least 13 US states have made efforts to increase the minimum wage

Analysis: Samira Hussain, BBC New York Business Reporter

I've been to several of these minimum wage protests and for the last year, the tone and message has been the same: workers marching, chanting slogans and holding up placards.

While the one held on Wednesday in New York during the lunch hour had all of those elements, it was also different.

I saw men and women sitting on a busy Manhattan street, blocking traffic, defying requests from police to move and subsequently getting arrested. A sign that the protestors and organisers are willing to turn up the intensity of this movement.

Given the successes they've already seen, with some 13 states making changes to their minimum wages, this comes as no surprise.

The question is whether they can continue to build momentum as the US heads into the mid-term election period.