TOKYO - A memorial service was held in Tokyo on Sunday to mark the one year anniversary of the March 11 earthquake and ensuing tsunami that left more than 19,000 people dead or missing and triggered a nuclear accident the world had never seen since 1986.?

Flowers for offering prayers for victims of the March 11, 2011 earthquake and tsunami are placed at a seaside which was damaged by the disaster in Iwaki, Fukushima prefecture, March 11, 2012, to mark the first anniversary of the earthquake and tsunami that killed thousands and set off a nuclear crisis. [Photo/Agencies]

A memorial service was held in Tokyo on Sunday to mark the one year anniversary of the March 11 earthquake and ensuing tsunami that left more than 19,000 people dead or missing and triggered a nuclear accident the world had never seen since 1986.

Attendants observed a moment of silence at 14:46 pm (0546 GMT), the exact time when the magnitude-9.0 quake struck the seas off northeastern Miyagi Prefecture a year earlier.

Emperor Akihito, who received a heart surgery last month, delivered a speech at the event in the National Theater in downtown Tokyo.

The emperor urged the Japanese people to work hard to improve the conditions in the quake-hit areas.

Prime Minister Yoshihiko Noda vowed at the ceremony to continue to make utmost efforts to realize speedy reconstruction of the zone devastated by the disasters.

"We will do our best to reconstruct Fukushima and create beautiful hometown," Noda said.

Noda also expressed his thanks to the international community for their assistance and help. The Japanese prime minister said he was committed to reviving Japan through rebuilding the quake-hit areas.

About 1,200 people, including representatives of those who lost their family members in the three hardest-hit prefectures, attended the ceremony.

Memorial services were also held in Iwate, Miyagi and Fukushima, the three prefectures hit hard by tsunami.