Boko Haram leader tape threatens Nigeria forces

* Second tape in three weeks claims Kano killings

* Purported Boko Haram leader says America fighting Islam

By Mike Oboh

KANO, Nigeria, Jan 27 (Reuters) - In an audio tape posted on the Internet, the purported leader of the violent Nigerian Islamist sect Boko Haram threatened to kill more security personnel and kidnap their families, and accused U.S. President Barack Obama of waging war on Islam.

In the 45-minute tape released on Thursday, a man's voice in the main northern Hausa language claimed to be Abubakar Shekau. He said President Goodluck Jonathan would fail to stop their insurgency.

Boko Haram's attacks have become more sophisticated and deadly in recent weeks in Africa's top oil producer. A series of gun and bomb attacks killed 186 people in Nigeria's second city of Kano last Friday.

"We were responsible for the attack in Kano, I gave the order and I will do it again and again. Allah gives us victory," the voice said.

If confirmed as authentic, the second tape in just under three weeks by Shekau would suggest he wants to use to media to establish his authority over the group, security sources said.

Shekau is said to have taken over control of Boko Haram, which wants sharia law more widely applied across Nigeria, after the sect's founder Mohammed Yusuf was killed in police custody in 2009 following an uprising in which 700 people were killed.