The ceremony held in a national assembly compound comes four months after the country held its second post-Taliban parliamentary elections, the results of which have met with massive controversy over claims of widespread fraud. [break]
"Congratulations," Karzai told the lawmakers after swearing them in with the placing of a hand on a copy of the Koran, watched over by government ministers, foreign diplomats and the head of US-led NATO forces in the country, General David Petraeus.
The embattled president had last week said he would delay the opening of parliament for a month to allow time for a special tribunal to investigate claims of irregularities in September parliamentary elections.
Meeting with hundreds of losing candidates in his palace on Tuesday, Karzai accused "foreign hands" of influencing his decision to go ahead with the ceremony.
"Some foreign hands questioned our decisions and started instigation to create crises in our country," Karzai said, according to a statement released by his office earlier.
They "kept provoking candidates (winning MPs) that they should inaugurate the parliament without the president´s participation and that we will support you," the statement quoted the president saying.
The elections have been controversial, not only because of the fraud that saw nearly a quarter of about five million votes thrown out, but also because of the relatively few wins by Pashtuns, Afghanistan´s biggest ethnic group and Karzai´s traditional powerbase.
Karzai has never endorsed the final outcome of the vote.
Afghanistan´s top prosecutor, Mohammad Ishaq Alako, an ally of Karzai has called for the annulment of the election results, saying his investigations found it was fraudulent.
Karzai has established a special tribunal to investigate claims of election fraud and has resisted demands by the new MPs to scrap the court. Newly-elected MPs say the tribunal is unconstitutional.
About 300 losing candidates met Karzai on Tuesday in his fortified palace to protest against his U-turn over the new legislature, and nearly 200 of their number camped out overnight at his office in an unusual show of defiance.
"About 180 to 200 of them refused to leave the palace and spent the night," a presidential aide told AFP from the palace, speaking anonymously because he was not authorised to speak to media.
"They say they´re protesting the president´s decision to open the parliament."
He said the protesters, mostly men, spent the night in a large hall within the heavily barricaded presidential palace in central Kabul.
On Tuesday former MP Daud Sultanzai accused foreign embassies and the UN of pulling the strings of the Afghan government.
The situation is being watched closely by the international community in Kabul -- 2011 is a key year for the war-torn country, with foreign troops due to start a limited withdrawal in July.
The United States, UN and European Union have all welcomed Karzai´s decision to relent and open parliament on Wednesday.
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