Pakistani police on Tuesday arrested 30 suspects and registered FIR against four unidentified terrorists in connection with a suicide attack outside Punjab assembly here in which 13 people, including six security officials, were killed.

"We have arrested 30 suspects in connection with the Lahore's Mall Road blast so far. Investigation is underway and we will reach the mastermind of this attack," Punjab Government spokesman Zaeem Hussain Qadri told reporters here, as the country mourned the victims of the Taliban-claimed attack.

Thirteen people were killed and over 70 others injured in the suicide blast which had targeted police officials.

Lahore Traffic Police chief Capt (R) Ahmed Mobeen and Senior Superintendent Police Zahid Gondal were among the six security officials killed in the attack.

The Jamat-ul-Ahrar faction of the outlawed Tehreek-i- Taliban Pakistan claimed responsibility for the attack.

The group had claimed responsibility for a blast on March 27 last year at Gulshan-e-Iqbal Park in Lahore that left 75 people dead, mostly Christians who were celebrating Easter.

Official funerals were held on Tuesday for the security officials in different districts of Punjab province.

The bombing is said to be the first suicide attack in Lahore in which two senior police officers lost their lives.

Punjab Chief Minister Shahbaz Sharif, Governor Rafique Rajwana and senior police and military officers offered funeral prayers to the slain security officials.

According to the FIR, four suspected terrorists reached outside the Punjab Assembly building on the Mall Road where a protest demonstration of chemists was underway.

"Police tried to stop a suspected terrorist, aged between 17 and 20, to reach near the police officers who were busy negotiating with the leaders of chemists to end protest when he blew himself up. His other accomplices, however, managed to escape," the FIR said.

Punjab police spokesman Niyab Haider said a joint team of police and intelligence agencies are investigating the blast on different aspects.

Inspector General Police Punjab Mushtaq Sukhera said the terrorists' target was police personnel.

"The protest of chemists provided an opportunity to terrorists to target the police officers," he said.

DIG Mobeen earlier had survived an attempt to his life during his posting in Balochistan.

On February 7, the National Counter Terrorism Authority had issued a threat alert saying a terrorist group had planned an attack in Lahore.

"After this threat alert we had provided extra security to the Governor s House, Punjab Assembly and Lahore High Court building located on the Mall," Punjab Law Minister Rana Sanaullah said.

He said the Lahore blast could be a conspiracy to stop the Pakistan Super League final at Qaddafi Stadium in Lahore on March 5.