In gender-equality Sweden, a grassroots movement defending women's right to wear hijab has split the nation, backed by politicians and celebrities while critics say it supports a symbol of female "oppression".

Hundreds of Swedish women have posted photographs of themselves wearing headscarves on social media sites to show solidarity with a heavily pregnant Muslim woman who says she was attacked outside Stockholm for wearing a veil.

Police are searching for witnesses to the incident, which is being treated as a hate crime, and has sparked a wave of online protest.

Leftist politicians and celebrities were among those who lent their support to the movement, dubbed "The hijab appeal", by tweeting pictures of themselves wearing the Islamic headscarf.

By Thursday, more than 2,000 people had posted pictures tagged with the "hijab appeal" hashtag on Instagram, mostly featuring women of different faiths wearing the veil.

A Facebook "event" page set up by the activists garnered 10,000 attendees but had to be removed after the comments section was swamped with racist and sexist remarks.

"The number of hate crimes against Muslim women has increased lately," one of the campaign organisers, Foujan Rouzbeh, told AFP.

However, critics say the campaign trivialises the suffering of women forced or pressured into covering their heads, in Sweden and elsewhere.

"I support protesting against the treatment of the woman who was attacked, absolutely. Holding speeches, demonstrating," said Sara Mohammad, the head of a charity for victims of honour crimes.

"Not by wearing the veil, which is known around the world as an Islamic symbol for oppressing women. It's not just being forced on women in Iran and Saudi Arabia, it has also become the flag for political Islam in the west."

The Swedish politicians wearing the hijab this week rarely displayed the same support for those fighting for the right not to wear it, sometimes risking their lives in doing so, Mohammad argued.

"This is an injudicious and populist measure designed to attract votes from the Muslim community," she said.

Rouzbeh said critics of the Swedish hijab campaign had taken it out of context.

"We're not trying to belittle people's experience of having been forced to wear the veil ...we're basing this on veiled women who wear it out of choice. Those women should have the right to do that without being attacked," she said.

Muslim women were being used as scapegoats in the face of rising unemployment in Sweden and the rest of Europe, said Rouzbeh, who met the justice minister on Wednesday.

"None of us are saying this started under the current government, but we would argue that it has increased because they haven't taken this threat seriously."

The group is demanding a commission be set up to investigate the problem of violence against veiled women, and also wants the government to ensure a ban on newsreaders for public broadcaster SVT wearing the garment is lifted.

Rouzbeh said the rise of the anti-immigrant Sweden Democrats, which the latest polls indicate would be the third largest party in an election, and a negative image of Muslims in the media had stoked violence and harassment of women wearing the hijab.

But there is little data to support claims of a surge in the number of Islamophobic hate crimes.

The Swedish National Council for Crime Prevention said 306 such crimes were reported last year, compared with 278 the previous year and 272 in 2008.

Social anthropologist Aje Carlbom of Malmoe University said Swedish attitudes towards the hijab were largely positive, unlike towards the full-face niqab sometimes worn by more conservative Muslims.

He said he was not aware of any rise in the number of people who opposed it.

"Ever since we began having immigration from the Muslim world, it's been claimed that (dislike of the veil) is increasing, that it's widespread, and so on," he said.

"I don't know why this is happening right now."