Egyptian authorities have closed the Rafah border crossing with the Gaza Strip 'indefinitely' for security reasons after a day of deadly nationwide violence, a security official told AFP news agenncy.

Hundreds of Palestinian travellers on Thursday were left stranded on both sides of the crossing, the only gateway into the Hamas-ruled Palestinian territory that bypasses Israel, witnesses said.

The measure follows widespread unrest in Egypt on Wednesday after a bloody crackdown by security forces on loyalists of ousted President Mohamed Morsi.

The Egyptian authorities closed the border crossing for several days after the military overthrew Morsi on July 3. It later re-opened for four hours a day.

Hamas, the Palestinian branch of the Muslim Brotherhood, strongly denounced Wednesday's crackdown by security forces on protest camps set up in support of Morsi, who was a member of the political wing of Muslim Brotherhood.

At least 525 people were killed in violence across Egypt sparked by the crackdown, the health ministry said on Thursday.

Source: Agencies