When Michelle Obama joined US President Barack Obama on his visit to Saudi Arabia on Tuesday, many Saudis on Twitter focused on the fact that she was not wearing a headscarf rather than the outcome of the diplomatic visit.

The couple were visiting to offer condolences after the death of the late King Abdullah, and strengthen US ties with his successor King Salman. Members of the US delegation crossed party lines and included former Bush-era officials, according to AFP.

On Twitter, Saudis launched the hashtag #Michelle_Obama_NotVeiled in criticism of the first lady for not covering her hair.

In contrast to Saudi women, who are required to dress head-to-toe in black, Michelle Obama wore dark slacks and a blue top with her hair uncovered, reported AFP.

Saudis on Twitter also drew comparisons to Michelle's visit to Indonesia, where she covered her hair while visiting Istiqlal Mosque. They argued that, as the first lady was paying tribute to the late King Abdullah, she should also have covered her head in respect.

Saudi Arabia is considered to be home to Islam's holiest sites, while the king is called the "Custodian of the Two Holy Mosques".

However, some Saudis on social media also said that they understood that it was a short visit, and urged others not to criticise the wife of the kingdom's most important ally.

One woman even asked her fellow Saudis on Twitter not to "make Obama angry at us".

The United States and the Kingdom of Saudi Arabia have longstanding ties and remain bound by shared interests in regional stability and oil, according to AFP.