GAZA CITY, Gaza Strip – Hamas leaders went underground yesterday, fearing a “decapitation” campaign by Israel as the state stepped up pressure on the Palestinian Arab leadership.

Earlier an Interior Ministry building was hit by a powerful bomb that plunged through the roof and four floors. Ministers are now trying to avoid going to their offices.

“Of course I am scared,” Yousef Mosa Rizqa, who believes he may be targeted as the Palestinian Authority’s minister of information, said. “I am taking precautions, but measures are limited because Israeli aircraft carry the most sophisticated technology for killing. In the end, we can only rely on God.”

Behind a desk in a windowless room on the ground floor of an anonymous building, Mr. Rizqa denied that Hamas leaders had any control over the actions of the Hamas militia that fired a rocket from Gaza into a school playground in the Israeli city of Ashkelon on Tuesday night. No one was hurt in the attack, but it proved the homemade rockets used by terrorists now have a seven-mile range.

Prime Minister Olmert, who hinted on Tuesday that Hamas politicians might join Hamas fighters as targets for assassination, described the strike as “an escalation without precedent.”

“The rules of the game in dealing with the [authority] and Hamas must be changed,” he said.

But Mr. Rizqa said: “This [attack] was a surprise for us.The position of the government is to establish a state of calm between the two sides.”