An Egyptian court has remanded to custody the daughter and son-in-law of Yusuf al-Qaradawi, the chairman of the International Union of Muslim Scholars who is in exile in Qatar, a judicial source told Anadolu news agency on Monday.

Ola al-Qaradawi and her husband, Hossam el-Din Khalaf, were set to be released after being detained for 15 days. Instead, their detention will continue.

They are accused of being "members of an illegal organisation" - referring to the Muslim Brotherhood, which is banned in Egypt and for "planning terrorist action against the security of public institutions".

READ MORE: What is the Muslim Brotherhood?

Family lawyer Ahmad Abu el-Ela Madi told Anadolu that the couple was arrested on June 23 near Sahel al-Shamali on Egypt's northern coast, while on holiday for Eid-al-Fitr, a festival that marks the end of the Muslim holy month of Ramadan.

Egypt, along with Saudi Arabia, Bahrain and the United Arab Emirates, cut ties with Qatar on June 5, accusing it of supporting "terrorism". The four countries have not provided any evidence for their claim and Doha has repeatedly denied the accusation.

The Saudi-led group of countries has also accused 59 individuals and 12 charities in Qatar of being "linked to terror", allegations that Doha called "baseless" and "slanderous".

The list included Yusuf al-Qaradawi, a long-standing member of the Muslim Brotherhood.

Founded in Egypt, the Muslim Brotherhood is the oldest political Islamist group in the Arab world.

In 2012, it backed the candidacy of Mohamed Morsi, Egypt's first democratically-elected president. But following Morsi's overthrow in a military coup, the group was outlawed by the government.