IT IS becoming a familiar ritual: each time a significant anniversary of Argentina's 1982 war with Britain over the Falkland Islands looms, its government starts rattling sabres. In 2007 Néstor Kirchner, the country's then-president, cancelled an oil-and-gas agreement with Britain and banned energy companies active in the islands, which Argentina calls the Malvinas, from operating on the mainland. With the war's 30th anniversary falling in April, the tradition has been upheld by Cristina Fernández, Mr Kirchner's widow and successor, who is due to step aside for 20 days on January 4th 2012 in order to receive treatment for thyroid cancer. On December 20th she got Argentina's partners in the Mercosur trade block—Brazil, Paraguay and Uruguay—to declare that they would ban civilian ships flying the Falklands' flag from entering their ports. Although up to $300m in maritime trade to and from the Falklands passes through Uruguay each year, this decision may have little practical effect. Most of the 30 or so vessels hoisting the Falklands' flag—a British red ensign with a coat-of-arms featuring a ram and tussock grass—belong to Spanish fishing companies. British merchant ships will still be allowed to dock in South American ports. Nevertheless, the new Mercosur policy is the latest in a string of small diplomatic victories for Argentina, which is keen to regionalise what has always been a bilateral dispute. Mercosur already does not welcome in its ports British warships on Falklands duty. Earlier in December a meeting of the newly formed 33-country Community of Latin American and Caribbean States unanimously backed Argentina's “legitimate rights in the sovereignty dispute” over the Falklands and South Georgia. UNASUR, the putative South American union, has done likewise. In 2010 Hillary Clinton, America's secretary of state, called for talks over the dispute, a contrast to 1982 when the United States backed Britain. The British government insists that its control over the islands, which dates back to 1833, is clear under international law, and that the right of the Falklanders to self-determination is not negotiable.

Ms Fernández has been especially exercised by recent oil exploration in Falkland waters. The small deposits found so far may not be profitable, though a rig will shortly start to drill in previously unexplored blocks to the south of the islands. But Argentina responded to the resumption of drilling in 2010 by requiring ships travelling between the islands and the mainland to receive permission. In a speech at the UN in September, Ms Fernández threatened to disrupt the weekly flight between Chile and the Falklands, operated by Chile's LAN. She accused David Cameron, Britain's prime minister, of “mediocrity and near-stupidity” for refusing to negotiate sovereignty.

Argentina has forsworn another attempt to seize the islands by force. It anyway lacks the military means. Despite cuts in public budgets, Britain still spends heavily on the islands' defence.

But if oil starts to flow, Argentina might seek regional support for an economic blockade. Would it get it? Most Latin American governments are left-of-centre, strongly nationalist and increasingly confident of their growing clout in the world. Argentina has persuaded them that the Falklands are a colonial anachronism.

Mr Cameron said in a Christmas message that he would “never” negotiate on sovereignty “unless you, the Falkland Islanders, so wish.” The 3,000 islanders do not: as a people, they have been in the Americas as long as many Argentines, and they resent being bullied. But they—and Britain—have failed to explain their case to the rest of South America. British diplomats doubt that the region will offer more than rhetorical support to Argentina's claims. That looks complacent.