A Danish woman, who allegedly refused to take off her niqab, the religious outfit covering face and full body, has been deported from the Brussels airport after police were unable to identify her, a Belgian official said.

Theo Francken, the Belgian State Secretary for Asylum and Migration, confirmed the incident on Saturday on his official Twitter account.

"A Danish citizen coming from Tunis refused to take off her niqab at our border. Police could not identify her. She was sent back to Tunis," Francken tweeted.

He did not identify the woman by her name.

"Thursday I informed my Danish colleague Inger Stojberg, Danish minister for immigration, integration and housing] about the niqaab-incident with a Danish citizen on our Schengenborder," he added.

In November 2015, police in Brussels briefly held a Saudi woman wearing a niqab.

Niqab banned since 2011

A law banning women from wearing the full-face veil, niqab, and burqa, which also covers the eyes, came into force in Belgium on July 23, 2011.

Women wearing full-face veils in public are subject to fines and can face up to seven days in jail in the country.

The European Court of Human Rights (ECHR), the top human rights court in Europe, upheld Belgium's ban in July, rejecting a complaint by two Muslim women who wear the niqab.

The court based in Strasbourg said that the law was not discriminatory and did not violate the right to respect for private and family life, nor freedom of religion.