GAZA CITY, Gaza Strip — Israeli forces shelled the United Nations headquarters in the Gaza Strip today, setting fire to the compound filled with hundreds of refugees as U.N. chief Ban Ki-moon was in the region on a mission to end Israel's devastating offensive against the territory's Hamas rulers.

Ban expressed "outrage" over the bombing. He said Israeli Defense Minister Ehud Barak told him there had been a "grave mistake" and promised to pay extra attention to protecting U.N. installations. The Israeli military had no immediate comment on the bombing, which a U.N. official said injured at least three people.

Even as a top Israeli envoy went to Egypt to discuss a cease-fire proposal, the military pushed farther into Gaza in an apparent effort to step up pressure on Hamas. Ground forces thrust deep into a crowded neighborhood for the first time, sending terrified residents fleeing for cover.

Shells also struck a hospital, five high-rise apartment buildings and a building housing media outlets in Gaza City, injuring several journalists.

ISLAMABAD, Pakistan — Pakistan arrested more than 100 people in a crackdown on groups allegedly linked to the Mumbai attacks, a top official said today, adding that the information India has handed over still needs work before it can be used as evidence in court.Despite the announcement, Interior Ministry chief Rehman Malik dodged a question on whether Pakistan was conceding the plot that killed 164 people in India's commercial capital was hatched on his country's soil.India said a Pakistan-based militant group, Lashkar-e-Taiba, masterminded the November attack. In the days afterward, the U.N. Security Council declared that Jamaat-ud-Dawa, a charity in Pakistan, was merely a front for the outlawed militant organization.In a news conference, Malik said 124 people had been arrested, while authorities had taken steps against 20 offices, 87 schools, two libraries, seven religious schools, and a handful of other organizations and Web sites linked to the charity. He also said authorities had shut several relief camps of the charity, some of which have been alleged to be militant training grounds.