CARTAGENA, Colombia - President Obama, on a three-day trip to South America, attacked GOP frontrunner Mitt Romney's stance on immigration reform today, saying his support for Arizona's tough immigration law is "very troublesome."

"We now have a Republican nominee who said that the Arizona laws are a model for the country … and these are laws that potentially would allow someone to be stopped and picked up and asked where their citizenship papers are based on an assumption," Obama told Univision during an interview in Cartagena, where the president is attending the Summit of the Americas.

The three-day trip gives the president an opportunity to showcase his interest in the region and court Latino voters back home, whose support will be crucial in the upcoming election. Obama won a majority of the Latino vote in 2008 and his campaign is hoping for similar results come November.

If reelected, Obama vowed to tackle immigration reform.

"I can promise that I will try to do it in the first year of my second term. I want to try this year," Obama told Univision.

During his 2008 campaign, then-candidate Obama promised to produce an immigration reform bill within a year of taking office. The problem now, the president told Univision, is resistance from Republicans.

"The challenge we've got on immigration reform is very simple. I've got a majority of Democrats who are prepared to vote for it, and I've got no Republicans who are prepared to vote for it," he said.

"What we need is a change either of Congress or we need Republicans to change their mind, and I think this has to be an important debate during - throughout the country," he said.