Democratic presidential candidate Bernie Sanders is backing legislation that would let Americans sue Saudi Arabia over the 9/11 terrorist attacks.
The bill is opposed by the Obama administration but is important to families of 9/11 victims, some of whom believe Saudi officials played some part in the attacks.
Mr Sanders spoke in favour of the legislation on NBC's Today Show on the eve of the New York presidential primary.
He said it is important to have a full understanding of "the possible role of the Saudi government in 9/11".
US inquiries have not reported a link between the Saudi government or its senior officials and the attacks, but Mr Sanders noted that some conclusions remain classified.
Mr Sanders said Saudi Arabia promotes an extreme and "very destructive" version of Islam.
Fifteen of the 19 hijackers in the September 2001 attacks, which destroyed the World Trade Centre and killed thousands, were citizens of Saudi Arabia.
Mr Sanders is currently trailing former secretary of state Hillary Clinton in the race for the Democratic nomination with only a slim chance of overcoming her lead in delegates.
On the Republican side, billionaire Donald Trump is leading but may not have enough delegates to win the nomination before the party's convention this summer, leaving open the possibility of a floor fight to determine the eventual candidate.