Donald Trump said Thursday that if he is elected US president, he would support the Canadian Keystone oil pipeline project that was blocked by President Barack Obama on environmental grounds.

He also reiterated his intention, if elected president in November, to reverse much of Obama's energy plan and to "cancel" the landmark Paris climate pact of last December.

Speaking just after he won enough primary delegates to seize the Republican nomination for the White House, Trump told reporters that the project for a new pipeline to carry Canadian crude to the Gulf of Mexico "should be approved."

"I will absolutely approve it 100 percent, but I want a better deal," Trump added.

He said that because the project requires the US government to expropriate private land using eminent domain laws, the US should have a share of the profits.

"I'm going to say, folks, we are going to let you build the pipeline but give us a piece," Trump said.

"I want a piece of the profits for the United States. That's how we make our country rich again."

The Obama administration decided in October to deny TransCanada Corp. permission to build the 1,180-mile (1,900 kilometer) Alberta-Nebraska pipeline that would be a crucial link to carry heavy Canadian oil sands-derived crude into US markets and export terminals on the Gulf of Mexico.

Noting the high environmental cost of using the oil sands crude, Obama argued that approving the pipeline would harm the fight against climate change.

The decision, which came seven years after the company first submitted the project, marred US-Canada relations and angered many in the oil industry in both countries.

In January, TransCanada announced it would sue the US government for US$15 billion for blocking the project, saying it "was arbitrary and unjustified" under the North American Free Trade Agreement and also exceeded Obama's powers.

But the plunge in crude oil prices beginning in 2014 had already lowered the economic justification for the pipeline, with a number of oil sands investments cancelled and existing pipelines beginning to struggle for business.

Trump meanwhile reiterated his intention to reverse energy and climate change policies set by Obama, including US backing for the world's first universal climate change agreement by 195 countries, achieved in Paris on 12 December.

"We are going to rescind all the job- destroying Obama executive actions, including the climate action plan," Trump said.

"We're going to cancel the Paris climate agreement, and stop all payments of United States tax dollars to UN global warming programs."

Trump said he wanted to keep the US energy-independent, suggesting he would offer support to the fracking industry that has been the source of a large surge in US domestic oil production in the past five years, but has been hit hard by the collapse of global crude prices.

"We'll open it up. Be energy independent. We'll have all sorts of energy. We will have everything you can think of including solar," he said.