The Argentinian president has accused Britain of taking her country's resources and ignoring UN resolutions as the Foreign Office condemned a move by a South American trading bloc to ban boats with a Falkland Islands flag from its ports.

Tensions over the long-disputed territory erupted into the open after the decision by Mercosur, a trading bloc that includes Argentina, Uruguay, Paraguay and Brazil, to target boats with the "illegal" flag of the Falklands. An FCO spokesperson said Britain was "very concerned" by what it saw as the "latest Argentine attempt to isolate the Falkland Islands people and damage their livelihoods, for which there is no justification".

But the Argentinian president, Cristina Fernandez de Kirchner, welcomed the ban, thanking her regional allies for their "solidarity" and lambasting Britain for its position in the long-running dispute. While refraining from calling for the islands to be declared Argentinian, she asked for fresh talks on the status of the islands.

"The United Kingdom is a permanent member of the UN security council yet they do not respect a single, not a single resolution," said Kirchner in a speech at the Mercosur summit in the Uruguayan capital, Montevideo. "We are not asking them to come here and recognise that the Malvinas are Argentinian but what we are saying is for them to comply with the United Nations, sit down and talk, talk, talk."

She added: "Nor should they come at us with the excuse of the dictatorship or the war from 30 years ago because they were the ones who would speak with the dictators."

Kirchner also attacked Britain's oil and gas exploration near the archipelago, citing it as a reason why South American countries should join forces against the Falklands. A UK company struck oil there for the first time last year, raising tensions with Argentina nearly three decades after the two countries went to war.

"You should know that when you are signing something on the Malvinas in favour of Argentina you are also doing it in your own defence," said Kirchner, addressing other members of the trading bloc. "Malvinas is not an Argentine cause; it is a global cause, because in the Malvinas they are taking our oil and fishing resources."

The Foreign Office condemned the Mercosur declaration, according to which the bloc's four full members vowed "to adopt … all the measures it is possible to impose to impede the entry of boats flying the illegal flag of the Malvinas [Falkland] Islands."

"It is not immediately clear what practical impact, if any, this statement will have, which mirrors the language already used by the Union of South American Nations in 2010," said an FCO spokesperson. "We are discussing this urgently with countries in the region. But no one should doubt our determination to protect the Falkland Islanders' right to determine their own political future."

At the Mercosur summit, the president of Uruguay, José Mujica, described the Falkland Islands as "a colonial British position" in South America. "We hold nothing against the UK," he said, "but we have a lot in favour of Argentina."

Mujica said his country would never impose a maritime blockade of the Falklands. But Roger Spink, president of the Falklands Chamber of Commerce, said the community already felt isolated. "If we were Palestine, the European Union would be up in arms," he told the BBC.