The al-Qaeda leader, Ayman al-Zawahiri, has accused the United States of "plotting" with Egypt's military, secularists and Christians to overthrow Islamist president Mohamed Morsi, in an audio recording posted on militant Islamist forums.

In his first public comments on the July 3 military coup, the Al-Qaeda boss, himself an Egyptian, said: "Crusaders and secularists and the Americanised army have converged ... with Gulf money and American plotting to topple Mohamed  Morsi's government."

In the 15-minute recording, Zawahiri also accused Egypt's Coptic Christian minority of supporting the Islamist president's toppling to attain "a Coptic state stripped from Egypt's south".

He attacked the interim vice president, Mohamed ElBaradei, as an "envoy of American providence".

Zawahiri, who once belonged to the Egyptian Islamic Jihad group, criticised Morsi's Muslim Brotherhood movement for going soft on applying strict Islamic law.

'Democratic failure'

Morsi's "Muslim Brotherhood government strove to please America and the secularists as much as it could, but they were not satisfied with it," said Zawahiri.

"They did not trust it (Morsi's government) because they did not forget the Brotherhood's slogan: 'Jihad is our war, and death in the path of God is our highest aspiration'," he said.

"The Brotherhood abandoned that slogan, substituting it with the slogan 'Islam is the solution,' but the Crusaders and secularists did not forget," he said.

"What happened is the biggest proof of the failure of democratic means to achieve an Islamic government," he said of the coup.

"I call for them to be united ... to make Islamic law rule."