N American leaders meet to discuss trade and immigration

Presidents Enrique Pena Nieto and Barack Obama held bilateral talks before the official summit

The leaders of the three major North American countries are meeting in Mexico to discuss trade, immigration, energy and other issues.

On Wednesday, US President Obama, Mexico's Enrique Pena Nieto and Canada's PM Stephen Harper are expected to hold joint and bilateral meetings.

Mr Obama faces stiff opposition from his own Congress on parts of his agenda on cross-border issues.

The three countries are in the midst of negotiating a trans-Pacific trade deal.

On Tuesday, Mr Harper arrived a day early for talks with Mr Pena Nieto. The two countries also signed an agreement to expand air travel between them.

Nafta legacy

Mr Obama arrived on Wednesday afternoon in Toluca, Mexico, a growing city near Mexico's capital, and held a meeting with Mr Pena Nieto.

After a working lunch, the three North American leaders will have their official meeting, then hold an evening press conference.

The summit among the three nations, sometimes known as the "Three Amigos", will highlight the changes to their economies in the 20 years since a major trade agreement among them, Nafta, took effect.

But further trade links among Canada, Mexico and the US remain subject to the negotiations of the Trans-Pacific Partnership (TPP).

Canadian PM Harper (left) arrived a day early to sign several agreements with Mr Pena Nieto

Canada and Mexico joined the negotiations of this wider trade deal among the Americas, Asia and Pacific island nations in the last two years.

White House officials have said Mr Obama will make it clear to Mr Pena Nieto and Mr Harper that TPP negotiations should be completed this year.

But parts of Mr Obama's own Democratic Party have pushed back against elements of the negotiations.

"He is pursuing an agreement - TPP - that explicitly protects American workers and the environment and that he believes would be highly beneficial to our economy and the middle class," White House spokesman Jay Carney told reporters on the flight to Mexico.

"That's the conversation he has and others have with lawmakers of both parties."

Mexico is also eager to hear about US immigration reform, as legal and illegal immigration to the US has a widespread economic effect on both countries and many migrants in the US have relatives in Mexico.

An estimated 11 million illegal immigrants live in the US, many of them from Mexico, although the pace of migration from Mexico to the US has waned.

Far-reaching immigration legislation was passed by the Democratic-controlled US Senate last year. But similar legislation has an unclear path in the Republican-controlled House of Representatives, despite Mr Obama's calls to pass comprehensive reform.

Canada's government has also been eager to hear the United States' final decision on whether it will allow an oil pipeline, known as Keystone XL, to be built to carry tar sand oil from Alberta in Canada to refineries in the US.

A recent US state department report raised no major environmental objections, but the department is waiting on comment from other US agencies before making an official recommendation to Mr Obama.

Mr Pena Nieto may also bring up revelations from leaks by Edward Snowden that the National Security Agency spied on the Mexican president before he was elected and gained access to former President Felipe Calderon's email system when he was in office.

The US has faced awkward questions about its intelligence programmes from the staunchest of allies since details of the NSA spying on foreign leaders was made public in the Snowden leaks.

Another source of tension between the two countries is the recent execution in the US state of Texas of a Mexican national convicted of murder.