A wave of xenophobia is blighting the lives of thousands of Syrian refugees in countries such as Egypt and Lebanon, where they are often blamed for anything that goes wrong.

In Egypt, Syrians are accused of taking sides and interfering in the country's political crisis, while in Lebanon they are accused of taking the jobs of Lebanese.

Three militants were killed in Egypt's Sinai peninsula on Wednesday when their car bomb detonated before they reached their intended target, security officials said.

The bomb went off as the assailants entered the north Sinai town of El-Arish, where two soldiers were killed in separate shooting attacks earlier on Wednesday, the officials said.

The United States has delayed plans to supply Egypt with an additional four F-16 fighter jets due to unrest gripping the country, the Pentagon said Wednesday.

"Given the current situation in Egypt we do not believe it is appropriate to move forward at this time with the delivery of F-16s," spokesman George Little told reporters.

Gunmen killed two Egyptian soldiers in the restive Sinai on Wednesday, security officials said, as the military chief called for mass rallies to back a crackdown on "terrorism and violence".

One soldier died of a bullet wound to the chest after gunmen fired at a checkpoint near the north Sinai town of EL-Arish, the officials said.

Egypt's army chief called Wednesday for public rallies this week to give him a mandate to fight "terrorism and violence," as Mohammed Morsi's supporters continue to protest against his ouster.

"Next Friday, all honorable Egyptians must take to the street to give me a mandate and command to end terrorism and violence," General Abdel Fattah al-Sisi said in a speech broadcast live on state television.

A blast Wednesday at a police station in a Nile Delta city killed one person and wounded 28, a medic said, in the latest incidence of violence sweeping Egypt since president Mohammed Morsi's ouster.

Mohamed Sultan, deputy head of the emergency services, told Agence France Presse an explosive device went off very early in the morning outside a police station in the city of Mansura, in Dahqaliya province.

Gas-rich Qatar, a strong backer of Arab Spring uprisings and supporter of ousted Egyptian president Mohammed Morsi, has joined international calls for his release from detention while expressing concern at violence sweeping Egypt.

State news agency QNA late Tuesday quoted a foreign ministry official as saying Qatar had voiced "concern over the developments in Egypt, especially with the increasing number of civilian victims.”

Senior aides held with ousted president Mohammed Morsi since Egypt's army toppled him nearly three weeks ago have asked their families for prison clothes, signalling possible charges, relatives said Tuesday.

Khaled El-Qazzaz, the former president's secretary for foreign relations, and top adviser Essam El-Haddad made the request in telephone conversations last Friday, their relatives told Agence France Presse.

Pressure grew Tuesday on Egypt's new leaders to release Mohamed Morsi from detention as clashes between supporters and opponents of the deposed Islamist president left 10 people dead.

The deadly clashes which also wounded dozens broke out on Monday, raged through the night and were continuing on Tuesday, a day after Morsi's family vowed to sue the military over his ouster.

Four people were killed in clashes between supporters and opponents of ousted Egyptian president Mohammed Morsi Monday, one in Cairo and three to its north, security and medical sources said.

Two people died in clashes in Qalyub, north of Cairo, and a third was killed when he fell under the wheels of a train as he tried to flee, the security source told Agence France Presse.