Scarlett Johansson has ended her role as global ambassador for Oxfam.

The aid group said it deemed the position "incompatible" with Ms Johansson's promotion of an Israeli firm that has a factory in the occupied West Bank.

The 29-year-old US actress appears in an advertisement for SodaStream, which is due to air during the NFL Super Bowl on Sunday.

The ad has already been seen more than 4.5 million times on YouTube.

The Hollywood actress has worked on behalf of Oxfam since 2005, but the British-based aid agency said she had stepped down due to her role with SodaStream.

SodaStream manufactures products for people to make fizzy drinks at home.

"Oxfam has accepted Scarlett Johansson's decision to step down after eight years as a global ambassador and we are grateful for her many contributions," the charity said in a statement.

"While Oxfam respects the independence of our ambassadors, Ms Johansson's role promoting the company SodaStream is incompatible with her role as an Oxfam global ambassador.

"Oxfam believes that businesses such as SodaStream, that operate in settlements, further the ongoing poverty and denial of rights of the Palestinian communities that we work to support.

"Oxfam is opposed to all trade from Israeli settlements, which are illegal under international law."

Super Bowl half-time ads usually see companies go all-out with expensive TV spots and are enjoyed by US viewers as a key part of the whole event.

Sunday's Super Bowl is not only the biggest sporting event in the United States, it is one of the biggest advertising events on the planet, when a record $4m (€3m) buys 30 seconds of airtime.

More than 110m television viewers, or a third of the population in the US, are expected to watch Sunday's game.

The game will see the Denver Broncos take on the Seattle Seahawks at MetLife Stadium, just west of New York.

The SodaStream ad had been banned by Fox for taking a swipe at Pepsi and Coca-Cola.

Ms Johansson became an Oxfam global ambassador in 2007, helping to bring media attention to the impact of natural disasters and raise funds to fight poverty and save lives.

She went to India and Sri Lanka to meet survivors of the Indian Ocean tsunami and in 2011 went to a Somali refugee camp in Kenya to see the impact of the severe drought.

Recently, she made a short video urging people to donate to Oxfam's Super Typhoon Haiyan appeal.