(AFP) - US President Donald Trump pledged stronger support for Nigeria's fight against Boko Haram jihadists Monday, while demanding greater trade access to Africa's largest economy.

After a meeting with Nigerian President Muhammadu Buhari, the first leader from sub-Saharan Africa invited by Trump to the White House, Trump said he was prepared to sell helicopters to the oil-rich country in addition to light fighter aircraft already agreed.

"These new aircraft will improve Nigeria's ability to target terrorists and protect civilians," Trump said during a joint press conference in the White House's Rose Garden.

Asked when the first deliveries of equipment -- including a dozen A-29 Super Tucano light fighter aircraft and unspecified helicopters -- would take palce, Trump replied: "Very soon."

"We're getting them approved. Part of the problem is you weren't allowed to buy helicopters in our country and now you are; I worked that out," he added.

"We make the best military equipment in the world. And our friends can now buy that equipment."

Buhari, visiting the United States on a mission to drum up more counterterrorism support and US business investment, thanked Trump for Washington's support to help rebuild the country's northeast, which has been under assault for nine years from Boko Haram.

"The United States of America has been to date the biggest contributor to the humanitarian response," said Buhari.

And Buhari diplomatically brushed off the controversy over Trump's alleged branding of Nigeria and other African nations as "shithole countries" in a January rant over immigration.

"I'm very careful with what the press says, other than about myself," Buhari told reporters.

"I'm not sure about the validity or whether that allegation against the president was true or not. So the best thing for me is to keep quiet."

- Trump: need access for US exports -

Trump told Buhari that in return for America's support, US exporters are "owed" more access to Nigerian markets.

"We look forward to growing our trade relationship based on the principal of fairness and reciprocity," Trump said.

"But we give Nigeria well over $1 billion in aid every year, and we have already started talking with the president about taking down the trade barriers -- very substantial barriers to the United States trading with Nigeria. So we think that we are owed that."

Trump also appeared to tie US support for Nigeria and other African countries to their backing for the joint US-Canada-Mexico bid to host the football World Cup in 2026.

The North American group faces one rival bid from Morocco, with the decision by world football's governing body FIFA to come on June 13.

"I hope all African countries and countries throughout the world, that we also will be supporting you, and that they will likewise support us in our bid along with Canada and Mexico for the 2026 World Cup," Trump said.

"We will be watching very closely, and any help they can give us in that bid we would appreciate," he said.

During the press conference, Trump also raised the issue of the killings of Christians, in an apparent reference to the April 24 attack on a central Nigerian church where 18 people, including two priests, were murdered.

"We are deeply concerned by religious violence in Nigeria, including the burning of churches and the killing and persecution of Christians," he said.

"We encourage Nigeria and the federal, state and local leaders to do everything in their power to immediately secure the affected communities and to protect innocent civilians of all faiths, including Muslims and including Christians."

© Agence France-Presse