Olympics officials promised to push for life bans for dope cheats on Tuesday, echoing calls from Michael Phelps and Michael Johnson as a bitter drugs row engulfed the Rio Games.

After Phelps said he was angry that convicted dopers were allowed to compete, the International Olympic Committee (IOC) said its president Thomas Bach backed lifetime suspensions from the Games.

Earlier, boos had rained down on tainted Russian swimmer Yulia Efimova, who was also slammed by America's Lilly King in a spat which echoed the Cold War rivalry.

But an IOC spokesman warned that lifetime bans from the Games were fraught with legal difficulty, signalling they may be hard to push through.

"The president said that for serious doping issues, he would still really like to see a life ban," said IOC spokesman Mark Adams.

"There are a number of options we can look at that would certainly I would imagine be one of them but this is all very much within a very difficult legal framework.

"It is something that the president is very keen on and it appears that the public is very keen on it is just a matter of finding a way that is legally sound."

That may not be enough to appease an increasingly restive cohort of athletes who have complained loudly about having dope-tainted competitors in Rio.

Track legend Johnson echoed Phelps on Tuesday when he told AFP that athletes with a record of doping should be shut out of the Olympics.

"I would love them to say that an athlete with even only one ban or one doping offence should miss an Olympics," the 1996 Olympics 400m and 200m champion said.

- Sonny Bill sidelined -

After beating Efimova in the 100m breaststroke, King lashed out at the Russians but she also said drug-tainted Americans, like sprinter Justin Gatlin, should not be allowed to compete.

"Do I think people who have been caught for doping offenses should be on the team? No, they shouldn't," said the 19-year-old.

Phelps, who will go for his 20th Olympic gold medal on Tuesday, gave his heavyweight support to his young team-mate.

"You're probably going to see a lot of people speaking up more. I think something needs to be done," said Phelps.

"It's sad that today in sports in general, not just only swimming, there are people who are testing positive who are allowed back in the sport -- and multiple times.

"It breaks what sport is meant to be and that's what pisses me off."

Doping has cast a long shadow over the Rio Olympics after a row over the participation of Russia since revelations of a state-orchestrated drugs regime.

Chinese swimmer Sun Yang, who served a doping ban in 2014, has also come under fire after Australia's Mack Horton called him a "drugs cheat". France's Camille Lacourt alleged on Monday that Sun "pisses purple".

Among Tuesday's events, Phelps will try to wrest back the 200m butterfly title from South Africa's Chad le Clos, and America's gymnastics ace Simone Biles will go for her first Olympic gold.

New Zealand's rugby hopes took a massive blow when superstar Sonny Bill Williams suffered a tournament-ending injury in their shock 14-12 opening defeat to Japan.

France won their first gold of Rio in the equestrian team eventing. French hero Astier Nicolas also took a silver in the individual event behind Germany's Michael Jung.

Chinese weightlifter Deng Wei won the women's 63kg category with a world record after Taiwanese rival Lin Tzu-chi pulled out amid reports of a failed dope test.

China's divers made it three out of three as Chen Ruolin won a record-equalling fifth gold medal in the women's synchronised 10m platform with Liu Huixia.

And French Open champion Garbine Muguruza became the latest big name to crash out of the tennis, after world number one Novak Djokovic and the Williams sisters doubles team.