A U.S. border guard fired shots Monday at three people trying to enter a sleepy town on the Quebec-Vermont border where the library famously lies partly in Canada and partly in the United States.

The U.S. Border Patrol said one of its agents stopped three people — two men and a woman — trying to cross the border where Rock Island, Que., blends into Derby Line, Vt.

When the agent tried to question them, they refused to answer and then attacked him, punching him. The agent then pulled his gun and fired twice while they fled, the border patrol said.

Police later captured a man and a woman — one in Canada, the other in the United States. One man remained at large, possibly wounded, the CBC's Dan Halton reported.

U.S. authorities questioned the two suspects while police on both sides of the border continued to hunt for the second man.

The border patrol would not provide the suspects' nationalities.