WASHINGTON (Reuters) - President Barack Obama will delay the start of his visit to Asia this week to attend a memorial service for soldiers killed in a mass shooting at a U.S. military base, an administration official said on Sunday.

Obama was due to have left the United States on Wednesday, but will now depart on Thursday, the official said. Obama's first stop in his 10-day Asia trip is Japan, before heading to Singapore, China and South Korea.

Thirteen people were killed in a shooting spree at Fort Hood military base in Texas last week, one of the worst such shootings in U.S. history. An army psychiatrist is being held in connection with the shootings.

The administration official said the memorial service, which will be held at Fort Hood on Tuesday, had required the White House to juggle Obama's schedule.

The White House has not released Obama's full schedule for this week so it was not immediately clear what he would now be doing on Wednesday. He had already been scheduled to lay a wreath at Arlington National Cemetery on November 11, Veterans Day, before flying off to Asia.

(Editing by Jackie Frank)