The march was diverted and wreath laying at the County Tyrone town's cenotaph was postponed after the area was sealed off.
"The Memorial commemorates those who have given their lives in service to King and Country since 1914".
In a break with tradition, Prince Charles laid the head of state's wreath at the base of the monument shortly after a two-minute silence at 11am.
Former Prime Ministers David Cameron, Gordon Brown, Tony Blair and Sir John Major also attended the ceremony.
All were dressed in sombre black outfits, adorned with the red poppy.
Prince Charles, Prince of Wales lays a wreath at the annual Remembrance Sunday memorial at the Cenotaph on Whitehall on November 12, 2017 in London, England.
The Festival of Remembrance began in 1927 and was originally meant to honour those who died in World War One.
For Royal-watchers, the Cenotaph ceremony will have been a significant moment, as the heir to the throne represents his mother in one of the key public duties of the year. Queen Elizabeth has already reduced her schedule, with official engagements dropping 22 percent from the 425 in her 2012 diamond jubilee year to 332 in 2016. Philip's equerry will lay his wreath, Buckingham Palace has said, while Charles will also lay his own wreath.
Charles has stepped in for the Queen at the ceremony twice before - in 1983 when she was in Kenya and in 1999 when the monarch had travelled to South Africa. It has since grown and now remembers all those who died in war in battles of the past and wars that are still ongoing.
The evening saw a Festival of Remembrance held at Albert Hall.
There were special performances by Melanie C, Alfie Boe & Natalie Lowe, Emeli Sande and others all in tribute to the armed forces.
The Duchess of Cambridge, Countess of Wessex and Princess Alexandra watched from a second balcony.