Foreign Secretary William Hague sought to calm diplomatic relations with Latin America amid mounting tensions over the Falkland Islands.
He raised the issue on a visit to Brazil, which is one of a bloc of countries which has banned ships sailing under the Falkland Islands flag from docking at their ports.
"The days of our diplomatic retreat from your region are over," Mr Hague declared in a speech, hailing Britain's "most ambitious" effort to build relations for 200 years.
"Our aim is that the United Kingdom should be at the centre of the networks of the 21st century, including in Latin America," he told his audience in Rio de Janeiro.
But though Britain backed a stronger role for the region - such as a permanent United Nations Security Council seat for Brazil - it would remain "frank" over issues such as the Falklands.
"We will always uphold UK sovereignty and the rights of the Islanders to self-determination, while valuing the ability to discuss these issues with Brazil in a framework that respects international law and human rights."
As the 30th anniversary of the 1982 conflict with Argentina over the islands approaches, London and Buenos Aires are engaged in increasingly bitter exchanges.
Prime Minister David Cameron yesterday accused Argentina of "colonialism" after a meeting of the National Security Council discussed the situation in the South Atlantic.
He said he wanted to send a "strong message" about the islands, which the Argentinians refer to as the Malvinas, following months of escalating rhetoric from Buenos Aires.