UPDATE:
The United Nations said Tuesday it would immediately send negotiators to Kabul to begin the process of establishing an interim government. Northern Alliance Foreign Minister Abdullah Abdullah said alliance forces had no choice but to enter the city despite opposition from other countries, including the United States. When the Taliban suddenly withdrew from the city Tuesday morning, disturbances by "irresponsible people" with weapons forced the alliance to march in and secure the city, Abdullah said. 

Pakistan is repeating its call for Afghan opposition forces to remain on the outskirts of the capital Kabul. Foreign Ministry spokesman Aziz Khan said the "Northern Alliance forces must not occupy Kabul." Islamabad also called for the capital to be placed under U.N. control, with a peacekeeping force to keep order in a "demilitarized" city.

European leaders are stressing the need for a new political regime to be installed in Kabul to fill the vacuum left by the retreating Taliban. UK Prime Minister Tony Blair said the West would not "walk away" from the Afghan people, saying it was with them "for the long term."

Northern Alliance fighters have killed as many as 600 people since they seized the northern Afghan city of Mazar-e Sharif on Friday, Western officials in the Uzbek border town of Termez have told CNN. CNN has not been able to independently confirm the deaths.

As they retreated, the Taliban took with them eight foreign aid workers -- four German, two Australian and two Americans -- accused of spreading Christianity in Afghanistan, according to the father of one of the aid workers. 

Kabul resident Saeed Abbas remembers the last time the Northern Alliance held power in his city, when factional battles turned it into a war zone. Abbas said he is afraid the same thing will happen if the Northern Alliance captures Kabul again.

Political leaders abroad struggled to keep pace with military developments Tuesday as Northern Alliance troops entered Afghanistan's capital, Kabul.

The U.N. refugee agency has begun shifting Afghan refugees from a temporary camp on the Afghan-Pakistan border to a permanent one farther inland. The Roghani camp, with a capacity of up to 40,000, is the first camp to be opened in Pakistan since a new wave of Afghans began fleeing in the wake of the attacks in the United States.

KEY QUESTIONS:

• Will the Northern Alliance fully occupy Kabul or will most of its forces remain on the city's outskirts?
• Who are the Northern Alliance and other key players in the political landscape of Afghanistan, and how could U.S. military intervention affect the balance of power there?
• Will the Taliban surrender or will they continue to fight, possibly launching a guerilla war out of Afghanistan's mountains?
• Where is Mullah Omar Mohammed, the spiritual leader of the Taliban? 
• What kind of government will replace the Taliban if the religious group is removed as the country's government? Will there be a U.N. or international peacekeeping force in Kabul?
• How are the citizens of Kabul reacting to the Taliban abandoning the city?
• How long will the U.S.-led military campaign in Afghanistan last?
• What is the goal of the U.S. airstrikes over Afghanistan?
• What is the key to the mission's success?What is the White House doing to prevent al Qaeda from airing what it calls "propaganda" on U.S. media outlets?