Kamala Harris and Donald Trump attend 9/11 ceremony hours after TV debate

President Joe Biden and Democratic Vice President Kamala Harris arrive at the Flight 93 National Memorial (Jared Wickerham/AP)

Relatives of September 11 victims have appealed to presidential candidates Kamala Harris and Donald Trump for accountability as the US marked an anniversary of the terror attacks laced with election-season politics.

President Joe Biden, former president Mr Trump and Vice President Kamala Harris stood together at ground zero just hours after the Republican and Democrat rivals faced off in their first debate.