The head of the International Cricket Council tribunal Michael Beloff announced the verdict after a lengthy nine-hour hearing in the Qatari capital.
"The Tribunal found that the charges under Article 2.1.1 of the (ICC) code that (respectively) Asif agreed to bowl and did bowl a deliberate no ball in the Lord's Test match played between Pakistan and England from 26 to 29 August 2010.
"Amir agreed to bowl and did bowl two deliberate no balls in the same Test, and Butt was party to the bowling of those deliberate no balls, were proved," said Beloff.
The tribunal then announced that 26-year-old Butt was banned for 10 years.
But it added: "Five years are suspended on condition that he commits no further breach of the code and that he participates under the auspices of the Pakistan Cricket Board in a programme of anti-corruption education."
Asif, 28, received a seven-year ban with two suspended on the same condition while 18-year-old Amir was handed a straight five-year ban.
The charges relate to alleged incidents during the Test against England at Lord's last year, when Britain's News of the World newspaper claimed the players were willing to deliberately bowl no-balls.
The newspaper alleged the three had colluded in a spot-fixing betting scam organised by British-based agent Mazhar Majeed.
The members of the tribunal heard the case for six days last month before deferring the announcement on the request of players' lawyers.
In a separate development on Friday, British prosecutors charged the three players as well as Majeed with corruption offences and summoned them to appear in a London court on March 17.
Saturday's decision followed much argument after the players' lawyers requested the verdict be adjourned as it could prejudice the criminal case.
The trio have repeatedly denied wrongdoing.
However the decision is sure to heap further scandal on the corruption-tainted sport, whose marquee event -- the World Cup -- starts in the sub-continent in less than a fortnight.
Cricket was badly hit by the menace of match-fixing in 2000, resulting in life bans on Pakistan's Salim Malik and Ata-ur Rehman, India's Mohammad Azharuddin and Ajay Sharma and South Africa's Hansie Cronje.
Butt, Amir and Asif became the first players banned over allegations of spot-fixing.
The players have 21 days to appeal against the sanctions in the Court of Arbitration for Sport, based in Switzerland.
Beloff made recommendations to the ICC to make "certain changes to the code with a view to providing flexibility in relation to minimum sentences in exceptional circumstances."
"The tribunal notes that it is for the ICC, whether and, if so when, the fully reasoned decision in respect of the breaches of the Code and of the sanctions imposed in consequence should be published.
"It is our strong and unanimous view that it is in the interests of all concerned in the world of cricket that publication should take place as soon as possible," added Beloff, without taking any questions from media.
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