Pakistani troops launched a long-awaited ground offensive into the Taliban and Al Qaeda stronghold of South Waziristan today, beginning what experts say will be the country's most challenging chapter yet in the war on terrorism.

Tariq Hayat Khan, secretary of the Federally Administered Tribal Areas, where South Waziristan is located, confirmed that the operation had begun but would not give details. On Friday, army Chief of Staff Ashfaq Kayani met with the country's top government and political leaders to brief them on the situation in South Waziristan and on the wave of violence that has swept over the country in the last two weeks.

According to Dawn, a Pakistani television channel, Kayani told those at the meeting that it was crucial to begin operations in Waziristan given the dramatic rise in terrorist attacks in the country. At least 175 people have been killed in the attacks, which have included a series of suicide bombings and commando-style raids on key security installations. Last weekend, a team of militants attacked the army's heavily fortified headquarters in Rawalpindi, a bold strike on what amounts to Pakistan's Pentagon. The attack left 19 dead.

For months, the military has been getting ready for a major offensive by hitting Taliban hide-outs, training camps and weapons caches with airstrikes from fighter jets and helicopter gunships, and by blocking the militant group's supply and escape routes. The Taliban has claimed responsibility for the recent wave of attacks across Pakistan, and has warned the violence would be ramped up if the government went ahead with the offensive in Waziristan.

Previous offensives waged by the military against Waziristan's militants sputtered. Operations in 2003 and 2004 were followed by cease-fires that merely allowed the militants to regroup and consolidate their authority in the region.

Analysts say the government currently has widespread support within the Pakistani population to launch the offensive. However, ensuring support from the tribal groups that live in the Waziristan region will depend on the level of damage to civilians and property created by the offensive, as well as how thousands of ethnic Pashtun villagers fleeing Waziristan are treated as they seek refuge. Amnesty International reported Friday that 90,000 to 150,000 South Waziristan Pakistanis have fled the region since July, when the military began bombarding Taliban hide-outs in the area.