UPDATE 1-Suncor's Sarnia refinery running at 70 percent

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CALGARY, Alberta, Jan 22 (Reuters) - Suncor Energy Inc (SU.TO) said on Tuesday its 70,000 barrel per day refinery in Sarnia, Ontario, was running at about 70 percent of capacity, with diesel supplies hit by a shortage of hydrogen.

Suncor spokesman Brad Bellows said the refinery's hydrogen supplier had shut down until at least Jan. 27, cutting needed supplies. He said the refinery was producing more "off-road quality" diesel fuel until it has sufficient quantities of the gas.

In November, Suncor wrapped up a C$960 million ($905 million) project to boost the amount of oil sands crude the refinery could process in order to lower feedstock costs.

Along with the hydrogen shortage, the startup of the revamped equipment has also hampered output at the facility.

"We are going through some operational challenges," Rick George, Suncor's chief executive, said on a conference call discussing the firm's fourth-quarter earnings on Tuesday. "It's a little bit slower on the startup than we would have hoped.

($1=$1.03 Canadian) (Reporting by Scott Haggett; Editing by Rob Wilson)