Saudi Arabian women will be allowed to drive cars, the King Salman ordered on Tuesday, ending an infamous conservative tradition seen as an emblem of the Islamic kingdom's repression of women.

The Arab state has been widely criticised for being the only country in the world that bans women from driving with arrests and fines handed to those who flout the law.

Despite trying to cultivate a more modern image in recent years, the driving ban has remained in force, staining Saudi Arabia's reputation among its Western allies, including the US and the UK.

But the royal decree on Tuesday ordered a ministerial body to give advice within 30 days and then implement the order by June 24, 2018, according to state news agency SPA.

The move must 'apply and adhere to the necessary Sharia standards', it said, referring to Islamic law. It gave no details but said a majority of the Council of Senior Religious Scholars, Saudi Arabia's top clerical body, had approved its permissibility.

The announcement was greeted with celebrations around the world with the Saudi ambassador to Washington, Prince Khaled bin Salman, saying it was 'an historic and big day in our kingdom'.

'I think our leadership understands that our society is ready. I think it's the right decision at the right time,' the ambassador said.

The US State Department welcomed the move as 'a great step in the right direction' and President Donald Trump commended the decision. The White House issued a separate statement that pledged US support for a plan the Kingdom announced last year for economic and social reforms.

'This is a positive step toward promoting the rights and opportunities of women in Saudi Arabia,' the White House statement said. 'We will continue to support Saudi Arabia in its to efforts to strengthen Saudi society and the economy through reforms like this and the implementation of Saudi Vision 2030.'

For more than 25 years, women activists have campaigned to be allowed to drive, defiantly taking to the road, petitioning the king and posting videos of themselves behind the wheel on social media. The protests brought them arrest and harassment.

Activist Manal al-Sherif, who was arrested in 2011 after a driving protest, took to Twitter following the king's announcement to express her relief. 'Today, the last country on earth to allow women to drive... we did it'. she wrote.

Latifa al-Shaalan, a member of the Shura Council, an advisory body, said the decision would strengthen women's employment in the private sector.

'This is an historic day and I cannot find the words to express my feelings and the feelings of thousands of Saudi women,' she said on Arabiya TV.

But women are still legally subject to a male guardian, who must give approval to basic decisions they make in education, employment, marriage, travel plans and even medical treatment.

Women in the kingdom are also forced by law to wear long robes and a headscarf and require the consent of a male guardian for most legal actions.

Prince Khaled, the ambassador, said women would not need permission from their guardians to get a licence or have a guardian in the car and would be allowed to drive anywhere in the kingdom, including the Islamic holy cities of Mecca and Medina.

Women with a licence from any of the Gulf Cooperation Council countries would be allowed to drive in Saudi Arabia, he added. He said the Interior Ministry would have to decide whether they could be professional drivers.

The position of Saudi women gradually improved under late King Abdullah and since King Salman took over in 2015, the kingdom has been opening more areas for women through the government's modernising reforms.

That has sparked tensions with influential clerics upon whose support the ruling family relies.

It wasn't long before a conservative backlash online accused the government of 'bending the verses of Sharia'.

One social media user posted: 'As far as I remember, Sharia scholars have said it was haram (forbidden) for women to drive. How come it has suddenly become halal (permissible)?'

Asked whether he was worried about the traditionalist response, the ambassador said: 'On these changes some people will be in the drivers' seat... some people will be in the back seat, but we're all going to move forward.'

He added: 'It's not women must drive, it's women can drive. So if any women do not want to drive in Saudi Arabia, that's her choice.'

Some leading members of the country's powerful and austere Sunni Muslim clergy have argued against women being allowed to drive, which they say could lead to them mingling with unrelated men, thereby breaching strict gender segregation rules.

The decision could also have broad economic impacts, making it possible for women to get to work without a driver but also curbing the popularity of car hailing apps like Uber and Careem.

Prince Khaled, a son of the king, said the decision was as much about economic reform as social change.

Additional reporting by Reuters.