Nigeria's MPs are investigating how $9.3m (£5.7m) of government money ended up on a private jet in South Africa.

Senate defence committee chairman Thompson Sekibo made the disclosure after a closed-door meeting with security chiefs.

South African authorities seized the cash from two Nigerians and an Israeli at an airport earlier this month.

A PR firm working for the Nigerian government says the money was for a legitimate arms deal.

The money, in $100 bills, had been stashed in three suitcases when customs officials at Johannesburg's Lanseria airport seized it from the two Nigerians and Israeli. They were not charged.

'Digging for details'

The BBC's Will Ross in Nigeria's main city Lagos says many people want to know if it is normal practice to fly so much of money in a private jet when buying arms.

Alarm bells rang even louder when it was revealed that the jet belongs to Ayo Oritsejafor, the head of the Christian Association of Nigeria, he says.

The cleric has denied any involvement in the deal.

Mr Sekibo said the senate committee was "digging" to get more details.

"We are still investigating. We have started the investigation. When we get through the investigation, we will brief you. The money belongs to Nigerian government," he told journalists.

The committee had met Nigeria's Chief of Defence Staff, Air Marshal Alex Badeh, and Chief of Army Staff, Lt-Gen Kenneth Minimah, to discuss the issue late on Tuesday.

Earlier, about 50 MPs stormed out of Nigeria's lower chamber, the House of Representatives, after a motion to discuss the arms deal was blocked.

The deputy speaker said that as it was an issue of national security it could not be broached.

PRNigeria - which has strong links to the security agencies in Nigeria and does communication consultancy for the military - quoted a source as saying the money was for a legitimate government transaction to buy weapons.

Nigeria's budget for security is around $6bn a year.

But analysts question whether the money is spent in a transparent manner after complaints from soldiers that they are poorly equipped in the fight against militant Islamist group Boko Haram.

The group has waged a brutal insurgency in north-eastern Nigeria since 2009 and caused international outrage in April when it abducted more than 200 schoolgirls.

In recent months, Boko Haram has captured several towns and villages in the north-east, saying it is establishing a caliphate.