VANCOUVER - On the surface, the US team are ticking along nicely in the Women's World Cup in Canada but a growing controversy over allegations surrounding goalkeeper Hope Solo are threatening to take the gloss off their performances.

The US came through unbeaten from the "Group of Death", which included three teams in the top 10, and have striker Abby Wambach in top form, while Solo is anchoring an air-tight defence.

The team have also rediscovered their swagger as they are cheered along by the World Cup's most vocal supporters and all the signs indicate the Americans are progressing nicely as they face Colombia in Edmonton in the knockout phase.

Solo's refusal to confront new allegations over a domestic abuse case, however, are causing unwanted headlines off the field.

US Soccer has kept her away from the media while lower profile team-mates have been pushed into the spotlight even though the goalkeeper has done some brilliant work, particularly in their opener against Australia.

As the Americans progress deeper into the tournament, the scrutiny is sure to increase along with questions as to why she has been allowed to play, despite allegations in a report by ESPN that she was the aggressor in a domestic abuse incident involving her half-sister and nephew.

When charges were dismissed earlier this year, US Soccer thought the controversy was put to rest but it is now threatening to become an even bigger distraction, with a politician questioning the decision to allow it to fester.

US Senator Richard Blumenthal last week called on US Soccer president Sunil Gulati to "conduct an investigation into Solo's case and reconsider her participation in the World Cup".

"Domestic violence is unacceptable, particularly for an athlete representing the United States of America on the global stage," he said in an open letter.

So far, Solo and her team-mates have not shown any hint of being distracted from the task at hand.

The Americans have not conceded a goal in 243 minutes and Wambach, the all-time leading scorer in women's football, is looking as dangerous as ever.

"We're starting to find our way," said US midfielder Carli Lloyd. "We just played three tough teams so now, going into the knockout phase, we should feel more confident.

"We should be better on the ball, hopefully create more chances, hopefully score more goals, and just kind of build each and every game."

REUTERS