Secretary of State Hillary Clinton on Friday defended new moves to engage anti-US leaders in Latin America as a way to check what she called "disturbing" Iranian and Chinese inroads in the region.

Clinton said President Barack Obama has had to take a new tack after his predecessor George W. Bush's efforts to isolate such leaders had only made them "more negative" toward Washington and more receptive to rival powers.

"I don't think in today's world ... that it is in our interest to turn our back on countries in our own hemisphere," Clinton told diplomats and other State Department staff.

She described the new world as "a multipolar world where we are competing for attention and relationships with at least the Russians, the Chinese, the Iranians," adding such countries can soon fill the void.

"If you look at the gains, particularly in Latin America, that Iran is making, that China is making, it's quite disturbing," the chief US diplomat said.

"They're building very strong economic and political connections with a lot of these leaders. I don't think that it's in our interests," Clinton said.

She did not explicitly refer to inroads by Russia, which said in March it could seek the short-term use of bases in Cuba and Venezuela.

Her answer was prompted by concerns aired by a retired State Department official about the Obama administration's overtures toward Venezuelan President Hugo Chavez, an elected leftist-populist anti-US firebrand.

Clinton said Washington -- which has also made overtures to communist Cuba -- was still exploring how to deal with Chavez, Nicaraguan President Daniel Noriega, Ecuadoran President Rafael Correa and Bolivian President Evo Morales.

Earlier this month, the United States welcomed Venezuela's move to restore full diplomatic ties between the two countries -- broken in September -- by returning its ambassador to Washington.

Obama and Chavez met at the opening of a 34-nation Americas summit and photos of the encounter showed the US leader smiling as he shook the Venezuelan's hand and patted him on the shoulder.

It was Obama's first encounter with the Venezuelan leader, which critics back home assailed as naive and "irresponsible".

Obama hit back, saying: "It's unlikely that as a consequence of me shaking hands or having a polite conversation with Mr Chavez that we are endangering the strategic interest of the United States."

But he stressed he still had concerns about Venezuela and Chavez's often heated rhetoric.

US ties with Ecuador and Bolivia remain tense over counter-narcotics.

Quito expelled two US diplomats who were probing alleged drug links with a former top official, which the Ecuadoran government denounced as interference in its domestic affairs.

The Bolivian government recently expelled the US ambassador to La Paz, Philip Goldberg, and the US Drug Enforcement Agency after accusing them of plotting against the government.

In March, a US diplomat in La Paz, Francisco Martinez, was expelled on charges of conspiracy.

The Israel Project, a non-profit organization independent of the Israeli government, said Iran is capitalizing on anti-US sentiment among South American leftist governments to make economic and military investments in the region.

It said Iranian President Mahmoud Ahmadinejad's visit to Brazil on May 6 is part of the effort.

It added that Iran's allies include Chavez and Morales.

"Over the past few years, Iran has also developed new political ties with Brazil, Cuba, Ecuador, Paraguay and Uruguay," according to the Israel Project.

"The alliances among Iran, Venezuela, and Bolivia are of particular concern because they account for almost 10 percent of global oil production, giving them a substantial bargaining position in the negotiation of global oil prices," it said.