Japan kept security tight across the country on Saturday as its largest contingent of troops to date left on a controversial mission to Iraq.
About 140 ground troops attended a dispatch ceremony before setting off from Chitose airport on the northern island of Hokkaido on a humanitarian mission that has been criticised as a violation of Japan's pacifist constitution.
They will join about 100 troops who are constructing a base near the town of Samawa in southern Iraq.
Security was stepped up at key sites around Japan on Friday, including government offices, US bases and nuclear power plants, to guard against a possible terror attack, a National Police Agency official said.
More police patrol cars than usual were was also seen on the streets of Tokyo, but police officials declined to comment on whether there had been a new threat against Japan.
Media reports last year said al Qaeda had threatened to "strike at the heart of Tokyo" if Japanese troops entered Iraq.
There were two late-night explosions near the Defence Ministry in Tokyo earlier this week, which police said could have been carried out in protest against the dispatch.
No damage or injuries were caused by the blasts. Kyodo news agency said a leftist group had issued a statement claiming responsibility and saying it wanted to prevent the troops being sent.