In a video posted on the internet on Saturday, Ayman al-Zawahiri, said that US and British forces had become bogged down in Iraq and "have achieved nothing but loss, disaster and misfortune".
The Egyptian , who is believed to be hiding in Afghanistan or Pakistan, said: "Al-Qaeda in Iraq alone has carried out 800 martyrdom operations in three years, besides the victories of the other mujahidin. And this is what has broken the back of America in Iraq."
Al-Zawahiri also called for the overthrow of Pervez Musharraf, the Pakistani president, who has survived several assassination attempts since allying himself with Washington. Pakistan has captured or killed hundreds of people said to be al-Qaeda members.
"Musharraf is fanning the flames of civil war in Pakistan on behalf of America in Waziristan and Baluchistan"
al-Qaeda deputy leader
Al-Zawahiri said in the video, which carried English subtitles: "The West which claims to support democracy ... is encouraging Musharraf to stay in power by any means after he demonstrated his aptitude at killing Muslims.
"I call on the Pakistani people to stand with Islam against the Zionist-Crusader assault ... and topple this bribe-taking treacherous criminal.
"Musharraf is fanning the flames of civil war in Pakistan on behalf of America in Waziristan and Baluchistan."
Zawahiri was referring to areas where the Pakistani government has fought tribal forces with ties to al-Qaeda and the Afghan Taliban.
"He [Musharraf] is inviting the Pakistani army to fight its own people and brothers and turn a blind eye to the Indian threat," he said.
Volley of messages
The 16-minute video by al-Zawahiri was the latest in a volley of messages by al-Qaeda's most prominent figures.
Al-Zarqawi said US dreams in
Iraq would be defeated
Abu Musab al-Zarqawi, the al-Qaeda leader in Iraq, said in an internet video earlier this week that US "dreams" in Iraq "will be defeated" and "what is coming is even worse".
It also came within the same week as an audiotape by al-Qaeda's leader, Osama bin Laden.
The video was first obtained by IntelCenter, a US contractor that provides intelligence services to the US government.
A US counterterrorism official, speaking on condition of anonymity in compliance with office policy, said it was part of al-Qaeda's continuing propaganda programme to demonstrate that the group remained relevant.
In his internet message last month, al-Zawahiri called for attacks on the West, urging strikes similar to those against New York, London and Madrid.