Mr Mehsud does not like to be photographed
The chief of the Pakistani Taleban, Baitullah Mehsud, has told the BBC his group was behind Monday's deadly attack on a police academy in Lahore.
He said the attack was "in retaliation for the continued drone strikes by the US in collaboration with Pakistan on our people".
He also claimed responsibility for two other recent deadly attacks.
Baitullah Mehsud said the attacks would continue "until the Pakistan government stops supporting the Americans".
Security officials are interrogating at least four suspects captured after the attack, police say.
Eighteen people, including two civilians, eight policemen and eight militants, were killed and 95 people were injured during the eight-hour battle to wrest back control of the academy, the interior ministry said.
Pakistan's interior minister earlier identified the Taleban as well as other extremist groups as possible perpetrators and suggested a foreign state could also be involved.
Baitullah Mehsud is the supreme commander of the Tehrik-e-Taleban Pakistan group (Movement of Taleban in Pakistan).
He operates out of a stronghold in the Pakistani tribal region of South Waziristan and the US state department recently issued a $5m (£3.5m) reward for his capture.
Speaking to the BBC by phone, he also claimed responsibility for two other attacks:
- A suicide attack on a security convoy, also on Monday, near the town of Bannu in North West Frontier Province, which killed seven security personnel
- An attack on the offices of a police station in Islamabad on 25 March
But he denied responsibility for the bombing of a mosque in north-west Pakistan on 27 March, in which at least 50 people died.
US DRONE STRIKES
Approx. 300 people killed in at least 30 drone strikes since Aug 2008
Drone strikes target tribal regions, mostly Waziristan
Hellfire missiles fired from unmanned Predator drones is main method
Baitullah Mehsud warned the attacks would continue in Pakistan and threatened future attacks on American soil, while he shrugged off the risk of "martyrdom".
American missile strikes are expected to increase in line with the newly announced US strategy for Afghanistan and Pakistan, says the BBC's Barbara Plett in Lahore.
Different Taleban factions in the border region, including Baitullah Mehsud's, have joined forces in readiness to confront the planned American troop increase in Afghanistan, she says.
Meanwhile, as the Pakistan government attempts to build a national consensus to fight the Taleban, it is faced with trying to overcome deep opposition among its people to an American role in that struggle.
Earlier on Tuesday, Pakistan's interior minister urged the country to unite against insurgents after the attack on the police academy in Lahore.
The brazen nature of the siege exposed the challenge facing Pakistan
Rehman Malik said the country had a choice between letting the Taleban take over and uniting to fight them - adding that Pakistan's integrity was "in danger".
He told reporters that the militants were believed to be fighters loyal to Mehsud and included an Afghan national.
The minister also suggested that a foreign country was interfering in Pakistan's domestic affairs.
"Some rival country, or some hostile [intelligence] agency is definitely out to destabilise our democratic forces," he said, in a possible reference to Pakistan's long-time foe, India.
Indian officials have condemned the attack on Lahore.
Gunmen seized the Manawan police training school on the outskirts of the city during a morning drill on Monday.
MAJOR PAKISTAN ATTACKS
27 March 09: Suicide bomber demolishes crowded mosque near the north-western town of Jamrud, killing dozens
3 March 09: Six policemen and a driver killed, and several cricketers injured, in ambush on the Sri Lanka cricket team in central Lahore
20 Sept 08: 54 die in an attack on the Marriott hotel in Islamabad
6 Sept 08: Suicide car bombing kills 35 and wounds 80 at a police checkpoint in Peshawar
Aug 08: Twin suicide bombings at gates of a weapons factory in town of Wah leave 67 dead
March 08: Suicide bombs hit police headquarters and suburban house in Lahore, killing 24
Helicopter gunships backed up troops who confronted the militants. They were armed with grenades and some are believed to have blown themselves up with suicide vests.
Our correspondent, who witnessed the aftermath, saw broken glass, bullet casings and body parts scattered over the floor of the academy.
The attack came days after US President Barack Obama pledged to put Pakistan, along with Afghanistan, at the heart of his fight against al-Qaeda militants.
He said "al-Qaeda and its extremist allies" were "a cancer that risks killing Pakistan from within".
US officials have pledged to help Pakistan target so-called "safe havens" for militants in Pakistan's north-west tribal region bordering Afghanistan.