Investigators probing the deadly suicide bombing outside Lahore high court on Thursday that killed 26 people and injured nearly 70 are focussing on the severed head of the attacker and a finger found some distance away from the site of the blast.

The bomber is believed to have been a man in his twenties who had a few days' stubble and was wearing a track suit. The man approached a police picket near the Lahore [Images] high court and blew himself up.

Most of the dead and injured were riot policemen who were deployed ahead of a planned anti-government protest by lawyers.

The attacker's head was found in an alley between the High Court building and the Supreme Court's registry in Lahore, a security official said. "One side of the head of the bomber, who had shoulder-length hair, was damaged," he told the Dawn newspaper.

City police chief Malik Iqbal said plastic surgeons at King Edward Medical University have partially reconstructed the head and are still working on it.

A severed finger was found on Friday morning at a spot about 115 feet from the blast site by investigators, who scoured the area again. The sleuths had to wind up their search on Thursday after darkness set in and heavy rains lashed the city.

The finger was found by a sniffer dog brought in from Islamabad. It was sent for DNA tests to establish whether it matched the severed head.

More body parts were also found as the anti-terror Special Investigation Group of the Federal Investigation Agency joined the probe. Special Superintendent of Police (Operations) Aftab Cheema said the bomber had packed 14 kgs of explosives and three kgs of ball bearings into his suicide jacket.

The ball bearings were larger than those used in earlier attacks and the explosive device too was larger than usual, the police said.

Meanwhile, constables who survived Thursday's attack recounted horrifying tales of the carnage caused by the attacker, who blew himself up shortly before lawyers were to march through the area to demand reinstatement of judges deposed during 2007's emergency rule.

One constable, admitted to the Services Hospital, said the explosion occurred when a police officer was trying to remove a white 'Suzuki' car parked on the roadside. "We don't let anyone park a vehicle near us. As soon as the official tried to open the door, the blast occurred," he said.

"We all fell on the road. I could not move my limbs. When I turned my head, I saw one of my colleagues badly burnt".

Most of the policemen were hit by the ball bearings, which also damaged several cars and killed a horse that was pulling a tonga.

Policeman Syed Imtiaz Hussain, who sustained injuries, said, "A man rammed into our ranks and soon after there was a huge explosion. I saw the bodies of other policemen burning. It was like hell".

Lawyer Khurram Latif Khosa said, "It was a very loud blast. I was one of the first who rushed out of the court and saw a man bleeding from his nose and mouth. He died minutes later. I saw about 50 to 60 injured policemen, bleeding, scattered everywhere. They were asking for water".