A historic building has been exploded in violence - plagued southwest Pakistan after a predawn militant attack on the building, officials say.The assailants shot dead the guard and entered the 19th century wooden Ziarat Residency after midnight and planted several bombs, senior administration official Nadeem Tahir said. They were armed with automatic weapons and detonated the bombs by remote control. The building is in Ziarat town, 80 kilometers southeast of Quetta, the capital of insurgency-hit Balochistan province. "The Ziarat Residency, which had its balcony, floor and front made of wood, has been totally gutted," AFP quoted Police official Asghar Ali as saying. At least four blasts were heard in the town, he said. One has been arrested but no group has claimed responsibility for the attack. On Thursday, separate incidents of violence left four people dead and injured several others in the southern Pakistani port city of Karachi. Security officials said the people were killed in incidents of firing and torture in different districts in Karachi. Thousands of people have lost their lives in bombings and other militant attacks since 2001 when Pakistan entered an alliance with the US on the so-called war against terrorism, according to local media. Since late 2009, there has been a surge in militant attacks in Pakistan and thousands more have been displaced by the wave of violence and militancy sweeping across the country.