US President Barack Obama Monday welcomed the leaders of Mexico and Canada for a North American summit taking place against a backdrop of a vicious drug war in Mexico and continental energy rows.

Mexican President Felipe Calderon and Canadian Prime Minister Stephen Harper arrived at the White House for a "Three Amigos" summit, a meeting which enjoyed its heyday under his predecessor George W. Bush but has faded somewhat since.

The talks will last only a few hours: the three leaders and top aides will open with a meeting, then Obama will host his guests for lunch ahead of a three-way press conference.

The summit typically focuses on border issues and attempts to better integrate trade under the banner of the North American Free Trade Agreement (NAFTA).

No major agreements are expected to be signed at the summit, diplomatic sources told AFP ahead of talks, which come just two weeks before the broader Summit of the Americas in Cartagena, Colombia.

Violence along America's southern border has cast a pall over US-Mexico trade, with drug cartels fighting for control of routes into the United States and Mexico complaining of arms purchased in the United States flowing south.

Through NAFTA, Canada is the largest market for US exports, followed by Mexico. The United States in turn is the largest market for both Mexican and Canadian exports.

The summit may also touch on the issue of energy, after Obama delayed a project to build the $7 billion Keystone XL pipeline to carry oil from Canada to the US Gulf Coast for further environmental and safety reviews.

Harper expressed "profound disappointment" at the decision and repeated warnings that he would look to other markets such as China to sell Canada's booming oil production.

Republicans, seeking political traction in election year, as gas prices rise, slammed Obama for the decision, saying the pipeline would promote energy independence, and quickly create thousands of construction jobs.

While energy and trade issues may prove nettlesome, security cooperation has been increasing between the three nations.

Closer ties began with the $1.6 billion Merida Initiative, which Calderon signed in 2008 with then-US president George W. Bush. The initiative provides funds for anti-drug operations in both Mexico and Central America.

On March 27, US Defense Secretary Leon Panetta met in Ottawa with Canadian Defense Minister Peter Mackay and the heads of Mexico's army and navy to discuss anti-narcotics operations.

"This is the first time we've done it, but certainly from the US perspective, we would hope it could be institutionalized, because these challenges are not going away," a senior US defense official traveling with Panetta said.

Calderon turned the Mexican military loose on drug trafficking cartels immediately upon taking office in 2006, but the violence has only grown, with the toll from drug-related violence rising to more than 50,000 people over that period.

Calderon leaves office in December after six years as president, with strong support in Washington for the policies he pursued.

But the Obama administration is already preparing for the future, and the possible victory of Enrique Pena Nieto of the Institutional Revolutionary Party (PRI) in Mexico's July 1 presidential election.

Recent polls show Pena Nieto with a commanding lead over the conservative National Action Party (PAN) candidate Josefina Vazquez Mota, with the leftist candidate Andres Manuel Lopez Obrador a distant third.

The PRI governed Mexico for 71 years until the PAN's Vicente Fox was elected president in 2000. Calderon is only the country's second PAN president.