Tensions between the United States and Mexico remain high after the shooting death of an illegal immigrant at the border last month. The incident comes as the U.S. Congress prepares to debate a proposal to build a new 700-mile fence along the border -- a plan some Mexican commentators have likened to the Berlin Wall.

U.S. agent Dora Doyle says patrolling the border region has become increasingly dangerous. Standing at the steel fence separating San Diego from Tijuana, Doyle pulls out a rock covered in a gasoline-soaked rag, which she says migrants lit on fire and hurled across the border.

Doyle says tensions along the border clearly have escalated. Assaults against agents have doubled since last year. And just since October, there have been more than 80 incidents involving agents.

U.S. officials say a rock-throwing incident sparked the confrontation that lead to the Dec. 30 shooting death of 20-year-old Guillermo Martinez Rodriguez. San Diego police investigating the shooting say Martinez was part of a group of migrants trying to scale a border fence.

Investigators say when the Border Patrol tried to intervene, Martinez threw a rock, nearly missing an agent's head. The agent then fired his gun. Border Patrol officials allege Martinez was a smuggler with a history of past arrests.

But Agustin Martinez says he was with his brother that night and that no rocks were thrown. He says the agent shot his brother in the back as they were running away.

The shooting sparked widespread condemnation in Mexico, and newspapers covered the story daily. President Vicente Fox ordered a full investigation and even sent Washington a diplomatic note.

Agustin Martinez says he wants his government to continue pressuring the U.S. about the shooting and to make sure the agent who shot his brother is punished. Officials in both Mexico and the U.S. say their investigations continue.

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