Image copyright AP Image caption The Native American issue came up again in a TV debate between the rivals last week

Two political aides have been accused of making offensive gestures linked to Native Americans to poke fun at a US Massachusetts senator's challenger.

Republican aides were recorded making "tomahawk chops" and war whoops at a campaign event, according to the Democratic Party.

They are said to have been mocking candidate Elizabeth Warren, who claims Native American ancestry.

Republican incumbent Scott Brown said he would not condone such behaviour.

Meanwhile, Ms Warren, a Democrat, faces problems of her own, amid questions about her legal work in support of an industrial conglomerate.

The Massachusetts race is among the most closely watched in the upcoming US election. Mr Brown won a special election in 2010, making him the first Republican in the liberal state's seat in nearly four decades.

The Massachusetts Democratic Party said the two men in the clip, filmed in Dorchester, were an aide to Sen Brown and an employee of the state Republican Party.

"The behaviour of his staff is completely inappropriate," a Democratic spokesman said.

Sen Brown told the Boston Globe newspaper "certainly that's not something I condone", while repeating the allegation that his challenger had claimed Native American heritage to further her career.

Ms Warren has denied benefiting from her background ever since it emerged earlier this year that she was listed as a minority in a Harvard Law School directory.

In a political debate last week, Sen Brown said: "Professor Warren claimed that she's a Native American and a person of colour, and as you can see she's not."

His campaign has released attack ads focusing on the allegation.

Ms Warren meanwhile is facing questions about her legal work to help an industrial conglomerate fight a requirement that it pay for retired coal miners' healthcare.

Such work could tarnish her image as a consumer advocate - she helped set up the Consumer Financial Protection Bureau.

Her campaign said in a statement the case had involved bankruptcy principles and that retirees' benefits were not in jeopardy.