WASHINGTON - The US State Department urged American citizens on Sunday to avoid going to Japan because of the powerful earthquake that damaged the Fukushima nuclear power reactors.

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In a travel warning the department said it had requested all nonessential US government personnel to defer travel and urged American citizens to avoid tourism and non-essentialtravel to Japan.

It said that strong aftershocks were likely for weeks after the 8.9 magnitude one that struck northern Japan two days ago, and that Japan remained at risk for further tsunamis from aftershocks. People have been told to stay away from low-lying coastal areas.

Temporary water and food shortages may occur in affected areas due to power and transportation disruptions, the department said in giving updated details. Telephone services have also been disrupted in some areas.

Rolling power outages are scheduled for the Tokyo metropolitan area and in northern and central Honshu, the State Department said.

US citizens living or traveling in Fukushima prefecture were advised to follow the local instructions and evacuate the area immediately because of the damaged nuclear reactors.

The department said flights have resumed at all airports closed by the earthquake, except Sendai, Sado, Iwate-Hanamaki, and Misawa Airports.

In Tokyo, most public transportation including trains and subways was operating, it said.

But many roads have been damaged in the Tokyo area and in northern Japan. In the far-northern Iwate prefecture, toll road highways are restricted to emergency vehicles only, it said.

In the Miyagi prefecture, government checkpoints have been established on damaged roadways.