TOKYO (AFP) - Organisers of Japan's Nagano Marathon said on Tuesday that they will go ahead with the race as planned this weekend, despite the blasts in Boston that killed at least three people and wounded more than 100.

"We will have closer communications with police and security officers to make sure the race takes place without any problems," said Mr Makoto Yajima, a spokesman for the marathon organisers.

More than 650 police and security officers will be involved, he said, adding that this number was unchanged by events in the US.

Authorities in the United States were on alert following the double blasts, which dredged up memories of the September 11, 2001 suicide attacks on the Twin Towers.

President Barack Obama said on national television that it was not yet clear who was behind the explosions at the marathon, a popular event that had around 27,000 registered entrants.

The Nagano Marathon is held annually in the city that played host to the 1998 Winter Olympic Games. Around 10,000 runners are expected to take part in the race on Sunday.

Marathon running is a popular pastime in Japan and many races are televised live across the nation.