Voters have begun casting ballots for candidates seeking the Democratic and Republican presidential nominations in a trio of Washington-area primaries.
Virginia opened its polls at 11am with Maryland and Washington DC opening at 12pm, in the so-called Potomac Primary, named after the river that runs through all three areas.
Opinion polls conducted ahead of the voting showed Republican John McCain and Democrat Barack Obama favoured to win the day.
Mr McCain, an Arizona senator, has a virtually insurmountable lead in the delegate count over his nearest rival, former Arkansas governor Mike Hukabee.
Senator Obama of Illinois and his White House rival, New York's Senator Hillary Clinton, emerged from last week's Super Tuesday showdown neck-and-neck, but he won all five contests staged since then and crept into the lead in the Democratic delegate count.
State primaries and caucuses allocate delegates to the national party conventions that will formally select presidential nominees ahead of the 4 November presidential election.
Virginia is the biggest prize of the Potomac Primary with 83 Democratic delegates up for grabs, while Maryland has 70 on offer.
The US capital, which is a district and not a state, has 15 delegates.
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