Niger's President Mahamadou Issoufou secured 92 percent of the vote in a controversial run-off ballot boycotted by the opposition, according to official results released Tuesday.

Sunday's election in the impoverished but uranium-rich country was marred by low turnout and the opposition boycott.

Issoufou's sole challenger Hama Amadou, imprisoned since November on shadowy baby trafficking charges, was flown to France for medical treatment days before the second round.

The electoral commission said Amadou won seven percent of the ballots cast.

President Issoufou responded to the announcement of his victory, saying: "During this mandate, I will devote all of my energy to respond to the aspirations of the Nigerien people."

Speaking from the presidential palace, he said that security, strengthening democracy and guaranteeing food supplies would be priorities, adding that he needed "the support of all Nigeriens".

"Let us come together, not waste our energy on vain quarrels," said the president, following the results of the divisive poll.

The poll pitted 64-year-old Issoufou, a former mining engineer nicknamed "the Lion", against Amadou, 66, a former premier and parliament speaker known as "the Phoenix" for his ability to make political comebacks.

Issoufou won 48.4 percent in the first round on February 21. Amadou scored just 17.7 percent in the initial vote.

Voter participation was a crucial issue following the opposition's boycott call.

The COPA 2016 opposition coalition said voter turnout was a mere 11 percent nationwide, despite an initial official estimate of 56 percent.

- 'Pointless quarrels' -

Amadou was forced to campaign from behind bars after being detained on November 14 on baby-trafficking charges he says were concocted to keep him out of the race.

Issoufou, who took office in 2011, campaigned on pledges to bring prosperity to the country and vowed to prevent further attacks from jihadists in its vast remote north, and from Nigeria's Boko Haram Islamists to the south.

However, just three days before the second round contest, Niger suffered two jihadist attacks -- one in the west claimed by Al-Qaeda's north African affiliate which killed three gendarmes and another by Boko Haram in which a senior army officer died.

Religious experts have warned that the ultra-conservative Wahhabist strain of Islam is taking hold in urban areas although Niger's government says it is "closely monitoring" the issue.

The run-up to the first-round presidential vote was marred by violence between supporters of the rival camps, the arrest of several leading political personalities and a government announcement that it had foiled a coup bid.

However, aside from the jihadist attacks, the run-up to the second round passed off largely without incident.

Addressing reporters on Sunday, Issoufou said: "We should avoid pointless quarrels. The winner, whoever he is, must think about bringing Nigeriens together beyond his own camp, because we face significant challenges."

The West African state, where three-quarters of the population live on less than $2 a day, has only had a multi-party democracy since 1990.

Uranium is the country's main export, with Niger ranked fourth globally after Kazakhstan, Canada and Australia.

After a tussle over the future of uranium mining, Niger and French nuclear energy group Areva agreed a deal on two uranium mines in May 2014.

In late 2011, Niger officially became an oil-exporting country, following the inauguration of a refinery in Olelewa, central-eastern Niger, that is run by the state with help from a Chinese company.