The purported leader of Boko Haram, the Islamist sect in Nigeria, has denied government statements the group is involved in peace talks and has said its spokesman Abu Qaqa has been captured by security forces.Nigerian President Goodluck Jonathan has said the authorities were in dialogue with Boko Haram via back channels and that this was helping neutralise the threat the sect posed.But Abubakar Shekau, the group’s leader, said in a video posted on YouTube on Sunday that no such talks were going on."Let it be clear that we never sought dialogue or to sit down with government agents or representatives ... they (Nigerian leaders) will never know peace while they attack our members.”The sect is widely considered to be the biggest security threat in Africa’s biggest oil exporter. It has been blamed for more than 1,000 deaths since its insurgency - which is aimed at carving out an Islamic state in northern Nigeria - intensified in 2010.Shekau also said the sect’s spokesman was being detained by the security forces."Our spokesman, Abu Qaqa is alive but with the security agents, but I believe strongly that after this message from me they may decide to kill him this night,” Shekau said.It was the first public statement on the matter by the militants since a raid, which it says led to Qaqa’s arrest but not his death.Senior security sources said on September 16 that troops had killed a man identified as "Anwal Kontagora, alias ‘Abu Qaqa’”, whose pen name is often used to claim responsibility for the sect’s pronouncements from its base in the northeast of the country.