Security forces in Zambia have seized weapons and arrested 11 people, including senior opposition figures, allegedly involved in an insurrection plot, the government has said.

The leading opposition candidate in last Thursday's presidential election, Brian Mundubile, was also found at the scene of the raid in the capital, Lusaka, according to the country's top civil servant Patrick Kangwa.

In an interview with the BBC, Mundubile dismissed the accusations as "total fabrications", alleging security forces staged an attempt on his life during a raid at his home on Friday.

With results from more than half of the constituencies announced, he is trailing incumbent Hakainde Hichilema.

Hichilema, who is running for a second five-year term, has 62% of the votes. Mundubile, one of 13 challengers, has 36%.

But the 55-year-old opposition leader had earlier claimed victory and alleged, without sharing the evidence, that there had been voting irregularities.

Giving details about the raid, Kangwa said the individuals arrested were connected to "military plans involving foreign nationals and illegal military training camps".

He added that they posed "a serious threat to state security" and held "high-grade military weapons", ammunition and other materials intended for use in an armed insurrection.

He alleged that shots were fired at law enforcement officers leading to an exchange of fire.

Mundubile however told the BBC that there was no militia at his home.

"It's unfortunate that senior government officials would present themselves before the entire nation to make such falsehoods," he told BBC Focus on Africa.

According to Kangwa, among those arrested were Patrick Mwansa, the husband of Tasila Lungu, the daughter of former Zambian President Edgar Lungu, and other politicians.

The suspects are being held in custody at various police stations in Lusaka.