Egypt has urged US authorities to exercise restraint in dealing with racially charged demonstrations in Ferguson, Missouri - echoing language Washington used to caution Egypt as it cracked down on Islamist protesters last year.

It is unusual for Egypt to criticise such a major donor, and it was not immediately clear why the government would have taken such a step.

Ties between Washington and Cairo were strained after Egyptian security forces killed hundreds of Muslim Brotherhood supporters following the army's ousting of freely elected President Mohamed Mursi in July 2013.

Western allies have voiced concern about the democratic credentials of President Abdel Fattah al-Sisi, the army chief who toppled Mursi and went on to win elections. The United States has, however, continued to provide military and other support to Cairo.

The Egyptian Foreign Ministry's statement on the unrest in Ferguson read similarly to one issued by US President Barack Obama's administration in July 2013, when the White House "urged security forces to exercise maximum restraint and caution" in dealing with demonstrations by Mursi supporters.

The ministry added it was "closely following the escalation of protests" in Ferguson, unleashed by the fatal shooting of an unarmed black teenager by a white policeman on Aug. 9.

Human Rights Watch said in a report last week Egyptian security forces systematically used excessive force against Islamist protesters after Mursi was ousted. Egypt said the report was "characterised by negativity and bias".