WASHINGTON (AFP) -- The United States said on Monday the Cuban government had cut off electricity to its diplomatic mission in Havana, accusing it of engaging in "bullying tactics."

"On Monday, June 5, at approximately 03:00 A.M., electricity to the main building of the U.S. interests section in Havana was cut off," State Department spokesman Sean McCormack told a press conference. "The U.S. interests section building is the only building in the neighborhood without electricity," he said, adding: "I wonder how that happened."

McCormack said that the United States had written to the Cuban government asking for power to be restored, and had also issued a request through the Swiss embassy, which represents U.S. interests. But as of Monday morning, "the power remains cut off and the U.S. interests section is operating on generator power."

The spokesman said work was continuing at the U.S. mission, including interviews with refugees, and said he believed the communist regime had cut power to punish Washington over its efforts to provide information to Cubans about human rights and other issues.

The move "has everything to do with their displeasure over some of the activities" at the U.S. mission, he said.

Cuba had also been periodically "turning down the spigot on the water supply," the spokesman said.

He said Cuba's strategy would have no effect on the US mission's efforts. "I would just say that the bullying tactics of the Castro regime aren't going to work." Asked if the U.S. planned to retaliate against the Cuban diplomatic mission in Washington, McCormack joked that if the Cubans had paid their electricity bills on time to the local utility, "I think they're probably OK."

Cuban President Fidel Castro has been irked by a huge electronic billboard on the U.S. mission's facade, which runs messages promoting democracy and human rights.

In a bid to block views of the billboard, Cuba inaugurated a "mountain of flags" outside the U.S. mission building in February, featuring 138 black banners with white stars honoring Cuban victims of terrorism.

In Havana, a spokesman at the special interest section, Drew Blakeney, described it as "the latest example of harassment" against U.S. diplomats.

Blakeney complained that Cuban officials have denied them permits to import vehicles, prevented them from hiring Cubans for maintenance and cleanup jobs, and have refused to approve most of the visas for U.S. diplomats to work on the island. (Mccormack)