Guyana maintains that valid land borders were set in 1899 by an arbitration court decision.
Six police were wounded, President Nicolas Maduro told lawmakers.
The suspected shooter was detained, according to a police report.
Clashes with security forces at anti-government protests have left 125 people dead from April to July.
Trump's comment drew condemnation from Caracas, which called the threat "reckless" and "craziness."
The attack came just one week after the election of a constituent assembly
The movement scattered in various parts of the world is engaging in peaceful demonstrations against the new Constituent Assembly
The US measures came as Venezuela's opposition began a two-day nationwide strike
Donald Trump did not specify what measures could be taken.
Venezuela's Supreme Court meanwhile slapped an asset freeze and travel ban Wednesday on Attorney General Luisa Ortega
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