In the tape, al-Zawahiri played down US accomplishments in Afghanistan, saying it had just managed to move the Taliban government from Kabul to the mountains and countryside.
The tape aired by Aljazeera was produced by al-Sahab Productions, which usually distributes al-Qaida's videos.
The taped interview of al-Zawahiri had apparently been conducted to commemorate the fourth anniversary of the September 11 attacks on Washington and New York.
"What did they do? They drove Taliban's government out of Kabul, but it has been active in the mountains and countryside, where the real power of Afghanistan lies," al-Zawahiri said.
The al-Qaida deputy chief dismissed the legitimacy of the just-concluded Afghan parliamentary elections.
"The elections have been conducted under the terror of [Afghanistan's] warlords," al-Zawahiri said.
He added that northern Afghanistan and Kabul had become "an area of chaos, plundering, theft, violations and drug business" under American occupation.
"The elections were a masquerade more than anything else, as various regions of the country are under the control of highwaymen and warlords, and international observers ... cannot cover more than one tenth of the (electoral) districts," al-Zawahiri said.
He added that "the international mercenaries (UN observers) had seen only staged polls in some cities".
Counting of votes in Afghanistan's parliamentary elections began on Tuesday.
Counting of the ballots will
continue for the next two weeks
Trucks, helicopters and even donkeys were bringing the estimated 6 million ballots from far-flung regions for counting over the next two weeks to decide the makeup of Afghanistan's first new parliament in more than 30 years.
A spokesman for the Afghan-UN election board, Aleem Siddique, said the transportation of ballots to 32 counting centres nationwide was expected to be completed on Thursday.
Tallying of the votes, set to involve more than 7000 staff, had begun in several centres on Tuesday.
Afghan and international officials hailed Sunday's vote as a major step towards democracy after decades of war and turmoil, although initial indications were that the turnout was just more than 50% - compared with 70% in last year's presidential election, when 8 million voted, installing President Hamid Karzai.
Al-Zawahiri heaped praise again in Monday's tape on the 7 July London Underground blasts which killed 56 people, including the four attackers.
Ayman al-Zawahiri (R) is
Claiming responsibility for the blasts, he said the London bombings were carried out by the group to strike at "British arrogance".
"The London attack is one of the attacks that al-Qaida ... had the honour of carrying out against Zionist, British arrogance," al-Zawahiri said.
"This blessed attack revealed the real hypocritical face of the West," al-Zawahiri said in the tape in reference to British threats to deport anti-West Muslim clerics to their countries of origin.
Al-Zawahiri criticised the UN for turning a blind eye to the violations that took place in the Afghan elections.
"While the UN opposed the elections in Zimbabwe because the time for polling was inadequate, the organisation keeps silent on the elections in Afghanistan where the polling was carried out under the terror of the warlords.
Al-Zawahiri says the UN was silent
about Iraqi deaths under sanctions
"Even the ballot boxes remained in the hands of warlords, bandits and the US agents before they were deposited at the polling centres,'' he said.
He also criticised the UN for seeking to set up trials for alleged war criminals in Darfur, while ignoring more serious violations by the world's key players.
"The UN had been silent about the death of [a] million Iraqi children under the sanctions," he said.
The Egyptian-born al-Zawahiri also denounced US demands for political reforms around the world, including in Muslim countries.
He said "there is no reform without jihad for the sake of God and any call for reform without jihad will eventually be greeted by death and failure".
George Bush and Tony Blair are
accused of lying to their people
"Our enemies will not give us our rights without Jihad," he added.
''We should not be deceived by what had occurred in Georgia, Ukraine or Kyrgyzstan.
"Those were changes wanted by the Americans after they had prevented the Russians from interfering. Thus the Americans will never permit any Islamic regime to assume power in the middle of the Islamic world, unless such regime is in full collaboration with them, as the case is in Iraq."
Al-Zawahiri also accused US President George Bush and British Prime Minister Tony Blair of lying to the people.
"The London attack is one of the attacks that al-Qaida ... had the honour of carrying out against Zionist, British arrogance"
al-Qaida deputy chief
He alleged that the losses inflicted on the US-led forces in Iraq were much more than what the two government had been showing.
He called on all the armed factions in Iraq to unite against the invading forces.
"I urge the mujahidin (warriors of the holy war) to unite. It is a first priority now."
Al-Zawahiri also criticised efforts to integrate Palestinian resistance factions into the Palestinian Authority.
He said the invitation to resistance factions to participate in the parliamentary elections was an attempt to buy them off.
In addition, he strongly criticised the Pakistani President Pervez Musharraf for closing the religious schools in Pakistan and condemned Islamabad's close ties to the US.
Supporters of the Taliban government ousted by US-led forces in late 2001 for harbouring al-Qaida have stepped up assaults in Afghanistan this year, and more than 1200 people died in violence in the six months before the elections, many of them "militants".
Two rockets struck Jalalabad, the main city of eastern Nangahar province early on Tuesday, slightly injuring one person at a government building, Interior Ministry spokesman Yusuf Stanikzai said.
Another election board spokesman, Baheen Sultan Ahmad, said vote counting had not yet started in the province because of security concerns.
A roadside bomb exploded near a truck carrying ballots in Nangarhar shortly after polls closed on Sunday, but there was no damage to the vehicle or ballot boxes.
Initial indications were that voter
turnout was just over 50%
Although there were no major attacks to disrupt voting, officials believe the lower turnout may have been due to fears of Taliban threats of violence, the presence of regional commanders on the ballots and the bewildering choice of candidates.
Also, many Afghans distrust politicians they blame for plunging the country into chaos and are not convinced they can drag it out of poverty and pain.
Abdul Satar, a 50-year-old shopkeeper in Kabul, said he went to a polling place but marked his ballots with an 'X' as a protest.
"Warlords, illiterates, communists, Taliban," Satar said. "How can I believe these people will serve the country?"
"Warlords, illiterates, communists, Taliban. How can I believe these people will serve the country?"
Kabul shopkeeper Abdul Satar
In a preliminary report, a European Union observer mission gave the polling a positive review, but said vote secrecy was not always maintained.
It said shortcomings during the campaign included intimidation, intervention by officials, inadequate voter lists and "deplorable" killings of candidates and election workers.
Complete provisional results from the voting for parliament and 34 provincial councils are not expected for at least two weeks. Officials hope to have certified results by 22 October.