By Karolos Grohmann

RIO DE JANEIRO (Reuters) - A blanket ban on Russia at the Rio de Janeiro Games would have had devastating consequences, International Olympic Committee President Thomas Bach said on Tuesday, defending his organisation's decision to allow some Russians to compete.

The IOC opted not to ban all Russian athletes from the Rio Olympics after revelations of a wide state-backed doping programme across many sports.

Instead it chose a set of criteria for athletes to meet, including a clean doping past and sufficient testing at international events, that so far has allowed more than 250 out of the original 387 Russian athletes to be cleared for Rio.

Bach, speaking at the IOC session, said preventing clean athletes from competing and treating them as "collateral damage" would have been wrong.

"This blanket ban of the Russian Olympic Committee has been called by some the 'nuclear option' and the innocent athletes would have to be considered as collateral damage," Bach said.

"Leaving aside that such a comparison is completely out of any proportion when it comes to the rules of sport, let us just for a moment consider the consequences of a 'nuclear option'. The result is death and devastation...

"The cynical 'collateral damage approach' is not what the Olympic Movement stands for."

Several anti-doping bodies, including the World Anti-Doping Agency (WADA), as well as those from the United States, Canada and Germany, among others, had called for a blanket ban.

They expressed disappointment following the IOC Executive Board's decision to allow some Russians to compete and accused the Games' ruling body of lacking the leadership and courage to punish Russia.

POLITICAL PRESSURE

Russia's Olympic Committee chief Alexander Zhukov said he considered the IOC decision to be "very fair" given what he said was the pressure from several countries to ban his nation.

"We are witnessing the enormous pressure put on the IOC by governments and political circles of certain countries," Zhukov said, without naming them. "We are witnessing direct interference of politics in sport."

He said it would be tragic if any of the 250-plus Russians awaiting a final green light from the IOC after being cleared to compete by the international federations, were now sent home.

"If Russian athletes already in Rio ... are forced to leave then that will be a real tragedy. It will be ruined fates and broken lives of athletes."

Bach received the backing of the IOC members at the session in Rio for the executive board's decision that was taken last month.

Eighty-four members supported the decision not to impose a blanket ban with only one -- Britain's Adam Pengilly -- voting against.

Not even Dick Pound of Canada, an outspoken critic of the decision not to implement a full ban, opposed Bach and the executive board on Tuesday.

"The arrow has left the bow," Pound said, adding that it made little sense to oppose a decision that had already been taken.

"It (discussion) was not bad. It was the first time we had a chance to do this. There is some disconnect and we will have to bridge that gap but it is doable," Pound said.

Bach also rejected allegations the IOC was not determined to fight doping, saying the anti-doping system needed complete restructuring.

"Engagement and not isolation is the key to build a more robust anti-doping system," he said.

(Reporting by Karolos Grohmann; Editing by Toby Davis and Alison Williams)