US President Barack Obama has made a rare visit to Puerto Rico, marking the first official trip to the island by a sitting US president since 1961.

美国总统奥巴马对波多黎各进行了一次少有的访问，这是自1961年以来在任美国总统对该岛的首次正式访问。

He backed a referendum on the island's status, saying he would support any choice the Puerto Rican people made.

The 3.7 million residents of the US Caribbean territory are US citizens but cannot vote for the president.

The visit is being seen by some as an indirect bid for Puerto Rican votes in the swing state of Florida in 2012.

Mr Obama attended a Democratic National Committee event during his visit.

The president last visited the island in 2008 during his campaign for the Democratic nomination¹, promising² to return if elected president.

"Although my hair is a little greyer than during my first visit, I am glad to be able to keep that promise to the people of Puerto Rico," Mr Obama said as he greeted a crowd gathered in an aircraft hanger³（衣架，挂钩） .

As well as a behind-closed-doors Democratic fundraiser, Mr Obama met Puerto Rico's governor on Tuesday to discuss the political status of the territory.

In brief remarks before the meeting, Mr Obama told the crowd that when Puerto Rico had made a "clear decision" on their future political status, "my administration will stand by you".

The island territory has voted three times - in 1967, 1993 and 1998 - not to seek statehood or independence.

The Obama administration has asked Puerto Rico to hold two referendums（投票，公投） , the first on whether the territory should be independent or part of the US.

A second referendum would then ask Puerto Ricans if they would prefer the island to be independent, a US state, a free association or a commonwealth⁴.
Targeting voters

On Tuesday, Mr Obama also spoke⁵ briefly⁶ about the impact the economic crisis had on Puerto Rico, saying Puerto Ricans and Americans on the mainland shared the same concerns about the economy.

The BBC's Julian Miglierini in San Juan says many people there believe the visit is aimed at courting mainland America's Puerto Rican electorate⁷ - and Hispanic voters in general - as they could hold the key to Mr Obama's re-election in 2012.

The president has called for broad reform of the US immigration system, an issue affecting many Hispanics with ties to the 11 million US illegal immigrants.

Meanwhile, roughly 20 pro-independence demonstrators held an all-night vigil in San Juan ahead of the president's visit, calling for the release of three Puerto Rican nationalists imprisoned⁸ in the US.