"The United States must stand for the right of people to determine their own future," Gibraltar's head of government, Chief Minister Fabian Picardo said.
"I don't think there's anything in the American psyche that says that individuals like me and the Falkland islanders and the Gibraltarians should be told under whose sovereignty they will come."
Picardo is on a charm offensive — his fourth trip to the United States this year — in a bid to win international backing for Gibraltar and Britain in a festering diplomatic row with Spain.
The territory of 30,000 people perched on the southern tip of the Iberian peninsula bordering Spain this year marks the 300th anniversary of the Treaty of Utrecht which ceded its control to Britain.
But in recent months Spain has stepped up its long-standing campaign to wrest back the rocky and strategic promontory that overseas the gateway into the Mediterranean from the Atlantic.
"How can it be that the United States might not be concerned that there are 30,000 people in Gibraltar who are being bullied into changing their sovereignty?" Picardo asked at an event hosted in Washington.
"Issues like the Falklands issue and the Gibraltar issue create instability amongst those who should be allies," he argued.
"If we believe in the principle of self-determination then there is only one argument that the United States must defend that principle," he added, highlighting the position of US overseas territories such as Guam or Puerto Rico.
Picardo told news agency AFP that he hoped Washington, which has remained neutral in the row, would offer a statement backing the staunchly pro-British Gibraltarians right to self-determination.
And he said the territory was determined to fight back against what he called Spain's attempt "to choke the economy" by imposing stringent border and export controls leading to long lines at the frontier.
Madrid's actions raised questions about its bid to become a member of the UN Security Council, he alleged.
It was "a hypocritical example of how Spain is prepared to defend principles of democracy in the whole world, but won't defend it in her own backyard," he told AFP.
"In my view it really casts a question mark over their idea that should be one of the new members of the Security Council in 2015, when they themselves are causing a flashpoint over the Gibraltar issue."