About 50 MPs have stormed out of Nigeria's lower house of parliament after a motion to discuss an alleged South African arms deal was blocked.

Last week it was reported that government agents took $9.3m (£5.7m) in cash to South Africa to buy weapons.

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

The upper chamber has also summoned security chiefs over the issue.

Correspondents say the revelations have shocked many Nigerians and there have been calls for an inquiry.

South African police said last week customs officials seized the money in $100 bills in three suitcases that arrived on a private jet from Nigeria at Johannesburg's Lanseria airport earlier in September.

The two Nigerians and an Israeli allegedly did not declare the money and it was impounded.

However, they were not charged.

'Global trend'

Later, 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.

"Movement of cash for strategic purchase of security equipment by intelligence service is not new; it is a global trend," the source said.

The BBC's Haruna Shehu-Tangaza in the capital, Abuja says the MPs who stormed out were mostly from opposition parties, accusing the ruling People's Democratic Party (PDP) of blocking the motion via the deputy speaker, Emeka Ihiodioha.

They said the government owed the people an explanation over the source of the funds - as there is concern about corruption, he says.

It is unclear whether the security chiefs will appear on Tuesday before the Senate Committee on Defence, which issued its summons last week.

Soldiers fighting the Boko Haram Islamist insurgency in the north-east have complained that they lack adequate equipment and weapons.

Analysts say Nigeria faces restrictions buying weapons from some countries, including the United States, because of its human rights record.