US President John F Kennedy has been remembered as a transcendent leader of a rising nation at a ceremony in Dallas on the 50th anniversary of his assassination.

The Dallas event, the first official ceremony held in the city to mark the assassination, is one of a number of events taking place across the US.

Kennedy was remembered with prayers and a speech by Dallas Mayor Mike Rawlings, while military jets flew over the city's Dealey Plaza, where the president was shot.

"Our collective hearts were broken," Mr Rawlings told a crowd of about 5,000 people.

At Arlington National Cemetery in Virginia where Kennedy is buried, family members laid a wreath at his grave, where Jackie Kennedy and two of their children also are buried.

At dawn, Attorney General Eric Holder made a gravesite visit to honour Kennedy, bowing his head and placing a Justice Department commemorative coin at the stone.

Holder then walked a short path to the grave of Robert F Kennedy, who had served as attorney general under his brother.

The current attorney general bowed his head and left another coin.

At the John F Kennedy Library and Museum in Boston, a steady stream of people came in to view artefacts, including a video of Kennedy's state funeral and a display of the saddle, sword and boots of Jack Black, the riderless horse who had led the procession.

Hundreds of people also lined up to write their thoughts and sign their names in four large guest books set up at the museum on pedestals decorated with flowers.

Ireland remembers

The US Embassy in Dublin has marked the 50th anniversary of the assassination of President John F Kennedy with a wreath-laying and flag-lowering ceremony.

Tánaiste and Minister for Foreign Affairs Eamon Gilmore joined US Chargé d'Affaires Stuart Dwyer to lay wreaths at the base of the US flag as it was lowered.

Mr Gilmore described Kennedy as a "friend to Ireland and a statesman to the world".

Galway Mayor Padraic Conneely laid a wreath at a podium in Eyre Square where Kennedy addressed crowds during his visit to the city in 1963.

Other ceremonies have been held at the Kennedy Homestead, at the New Ross Quayside and in Limerick.