BAGHDAD (REUTERS) - A Shi'ite militia leader arrested in Iraq after his group fired mortars into Saudi Arabia has said leaders of Prime Minister Nuri al-Maliki's political bloc will be killed unless he is released within 24 hours.

Wathiq al-Battat, speaking on a mobile phone he said had been given him by a sympathetic prison guard, said he was being held without charge in solitary confinement in a small, cold cell, with no access to lawyers or his family.

Battat was detained in Baghdad on Jan 2, six weeks after his Iranian-backed al-Mukhtar Army fired six mortar bombs from southern Iraq into the Saudi desert, causing no casualties.

He said the attack was a warning to Saudi Arabia to stop meddling in Iraqi affairs.

In the call from his prison cell on Monday night, Battat said his Mukhtar Army would start killing members of Maliki's State of Law bloc running in April elections unless he is freed.

"The Mukhtar Army is giving them 24 hours," he said. "If I am not released all State of Law's candidates will be killed...one by one. Their homes and their headquarters will be targeted."

He said State of Law figures serving in the present government would also be on his hit list.

Iraqi officials could not immediately be reached for comment.

Battat, whose voice is known to Reuters, said he was hiding his identity from Sunni Muslim militants detained in the same prison, whose location he asked not to be mentioned.

"I am not a terrorist. I do not have a feud with the state or its institutions and I will not target the police or army.

"My targets are al-Qaeda and the takfiri country which exports terrorism to neighbouring countries," he said, referring to Saudi Arabia.

Opponents of Sunni hardliners sometimes describe them as takfiris, meaning those who condemn others, including Shi'ites, as apostates.

Battat accused the authorities of detaining him to make a"sectarian balance" after they arrested outspoken Sunni lawmaker Ahmed al-Alwani in the city of Ramadi on Dec 28 in a raid in which Alwani's brother and several bodyguards were killed.

Maliki has combated Shi'ite as well as Sunni militias since he took power in 2006 at the head of a Shi'ite-led government.