The UN Security Council voted unanimously to lift an arms embargo on rebel groups that was imposed 13 years ago to support a peace deal that ended a devastating war.
It was the last punitive measure in force from a sweeping series of sanctions that had included travel bans, assets freezes and a ban on lumber and diamond exports.
US Deputy Ambassador David Pressman said the decision showed "how far Liberia has come" in its transition to peace and marked the first time since 1992 that the country was not under UN sanctions.
"Targeted sanctions in the context of Liberia have been very constructive," said Patten.
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With the international measures now all lifted, Liberia has adopted gun-control legislation and is taking steps to strengthen control of its borders, he said.
The United Nations is also drawing down its peacekeeping mission in Liberia, UNMIL, which now has some 3,700 troops and police on the ground from its high point of 15,000.
The UNMIL mission helped Liberia during the deadly Ebola outbreak that killed thousands and brought the fragile health care system to its knees.
There is a sharp debate within the council on whether sanctions are a useful tool, with China, Russia and Venezuela arguing that they often fail to encourage better behavior.
Pressman argued that the council "must be creative and courageous in its sanction design," and pointed to the timber and diamond export bans in Liberia as a pressure tactic that could be applied to other conflicts.
Liberia has spent a decade recovering from two ruinous back-to-back civil wars that ran from 1989 to 2003, leaving a quarter of a million people dead and the economy in tatters.