Activists pushing for women's right-to-drive in Saudi Arabia have declared their online campaign a success, in the world's only country where women are not allowed to operate cars.

The campaign that began last year and revved up again since the beginning of the month encouraged women to post online images of themselves driving.

Dozens of women have driven and posted during the latest campaign, one activist said, although she knew of only two who hit the streets on Saturday and Sunday as the campaign peaked.

"A day hasn't gone by without receiving one or two videos" of women driving, said the activist.

Men and women have also posted messages of support.

More than 2,800 people have signed an online petition at www.oct26driving.com asking authorities to lift the ban on women driving.

The activist said she did not want to be named because the interior ministry has threatened her with arrest if she speaks publicly about the campaign.

There is a "huge risk" for female drivers, the activist said when asked why more had not posted images of themselves this year.

Women have previously been arrested, cars have been confiscated, and one received 100 lashes, she alleged.

"So, women are afraid," the activist said.

She added that, apart from driving, the campaign is also about "creating a storm" over the issue.

On Thursday the interior ministry issued a warning to would-be female drivers and their supporters.

The ministry said it would "strictly implement" measures against anyone who "contributes in any manner or by any acts, towards providing violators with the opportunity to undermine the social cohesion".

That means the campaign has had an impact, the activist said.

"I think it's pretty successful. If we're getting a reaction, that means we're effective."

Tradition and custom are behind the prohibition, which is not backed up by an Islamic text or judicial ruling, the online petition states.