(Reuters) - The leader of the Pakistani Taliban, the militant movement that poses the gravest security threat to the country, was believed killed by a U.S. drone strike, four Pakistan intelligence officials told Reuters Sunday.

The officials said they intercepted wireless radio chatter between Taliban fighters detailing how Hakimullah Mehsud was killed while travelling in a convoy to a meeting in the North Waziristan tribal region near the Afghan border.

A senior military official told Reuters there was no official confirmation that the Pakistani state's deadliest enemy had been killed. The Pakistani Taliban issued a denial.

If Hakimullah did die, it could ease pressure on security forces, who have struggled to weaken the group, which is close to al-Qaida and has been blamed for many of the suicide bombings across one of the world's most unstable countries.

But it may not improve security in the long-term in Pakistan, which is seen as critical for U.S. efforts to fight global militancy, most importantly in neighbouring Afghanistan.

The death of Hakimullah's predecessor Baitullah Mehsud in a drone strike in 2009 raised false hopes that the Tehrik-e-Taliban Pakistan, could be broken.

Six to seven TTP members were talking to each other through wireless radio in the conversations we heard, talking about Hakimullah Mehsud being hit by a drone when he was heading to a meeting at a spot near Miranshah, said one of the intelligence officials.

They referred to him by his codename. Officials refused to disclose Mehsud's codename.

Based on our intercepts, Mehsud was heading to a meeting in Nawa Adda, said another intelligence official. Nawa Adda is a village in the Dattakhel area of North Waziristan.

The Pakistani Taliban said Hakimullah was still alive, but their denial was far less assertive than one issued in 2010 after media reports said he had been killed in a drone strike.

There is no truth in reports about his death. However, he is a human being and can die any time. He is a holy warrior and we will wish him martyrdom, TTP spokesman Ihsanullah Ihsan said.

We will continue jihad if Hakimullah is alive or dead. There are so many lions in this jungle and one lion will replace another one to continue this noble mission.

(Reporting by Jibran Ahmad; Writing by Michael Georgy)