The bomber detonated an explosives-packed SUV near the outer perimeter wall of the Indian Embassy compound, killing at least 17 people _ all Afghans _ and wounding nearly 80 others including three Indian security guards. The Taliban claimed responsibility.
International efforts to end Afghanistan's violence are complicated because the major players see their interests differently. The U.S. goal is to prevent al-Qaida from regaining its bases in Afghanistan, where it trained militants and plotted the Sept. 11, 2001 attacks in New York and Washington.
Pakistan, with archrival India to the east, believes it needs a friendly government in Afghanistan on its western border, preferably one without close ties to the Indians. For its part, India seeks regional allies and access to oil- and gas-rich central Asia.
As the war enters its ninth year, President Barack Obama is considering whether to focus the fight in Afghanistan against al-Qaida's allies in the Taliban or shift to more missile strikes and special operations raids against al-Qaida in Pakistan, a nuclear-armed country where the terror movement's leadership is believed hiding.
Whatever option Obama chooses, the administration must wrestle with the fact that neither Afghanistan nor Pakistan can be secure as long as instability plagues the other. Militants move freely from one country to another, sheltering among the ethnic Pashtun community that lives on both sides of the border.
Pakistani tribesmen loosely allied with the Afghan Taliban have ambushed convoys carrying supplies to NATO forces in Afghanistan. Last spring, Pakistani Taliban moved into a district only 60 miles from the Pakistani capital of Islamabad, raising alarm until Pakistan's military drove them back weeks later.
"A valid Afghan strategy cannot be separate from what happens in Pakistan," former Pentagon analyst Anthony Cordesman said. "At the same time, it is clear that Afghanistan's future will play a critical role in defining Pakistan's security."
India too is at risk from Muslim extremist groups nurtured over the years by the Pakistani military to fight the Indians in Kashmir, a mountainous region straddling both countries and claimed by each.
The risks were highlighted Thursday in the Indian embassy attack.
The Taliban claimed responsibility in a Web site statement but did not say why the embassy was targeted. India's ambassador, Jayant Prasad, blamed the bombing on "people who don't like the friendship between the Afghan and the Indian people."
"We are working with our Afghan friends to find out more about who is behind the attack," he told The Associated Press.
However, the Afghan Foreign Ministry said the attack "was planned and implemented from outside of Afghan borders" by the same groups responsible for the July 2008 suicide bombing at the Indian Embassy that killed more than 60 people.
At the time, the Afghan government blamed the 2008 attack on Pakistan's Inter-Services Intelligence, although Thursday's statement did not mention Pakistan by name.
U.S. officials suspect the 2008 bombing was carried out by followers of Jalaluddin Haqqani, a longtime Afghan militant leader whose fighters are battling U.S. forces in eastern Afghanistan from sanctuaries in the border area of Pakistan. American commanders consider the Haqqani group, which is allied with the Taliban and has ties to al-Qaida, as among the most dangerous insurgent groups in Afghanistan.
At U.S. urging, the Pakistani military says it's planning an offensive against Taliban extremists in the border area of South Waziristan.
The Pakistani civilian governmet that took power last year has increased cooperation with the U.S. in the fight against Islamic extremists, and the Foreign Ministry spokesman, Abdul Basit, was quick to condemn Thursday's bombing in Kabul.
"Whenever terrorist activity occurs, it should strengthen our resolve to eradicate and eliminate this menace," Basit told reporters in Islamabad. He described speculation about a Pakistani role as "preposterous."
Nevertheless, some U.S. officials remain skeptical that the Pakistani military is prepared to break entirely with all the Islamic militant groups that operate in their country.
The Indian government refrained from affixing blame of Thursday's bombing, but many Indian defense and political analysts were quick to point the finger at Pakistan.
"How long is India going to absorb the shocks of repeated attacks?" asked Ajai Sahni of the Institute for Conflict Management, a New Delhi-based think-tank. He said the attack was the result of India's failure to develop "any conventional or covert strategy to impose any costs on Pakistan."
Another defense expert, C. Uday Bhaskar, director of the National Maritime Foundation, said India should send more security forces to protect Indian assets in Afghanistan.
Since the fall of the Taliban in the 2001 U.S.-led invasion, both Pakistan and India have competed for influence in Afghanistan. Over the last decade, India has poured nearly $1.2 billion into Afghanistan, helping fund projects such as a new Parliament building in Kabul, roads and power plants.
"Pakistan views India's growing influence in Afghanistan as a threat to its own interests in the region," wrote Jayshree Bajoria of the Council on Foreign Relations. "Afghanistan holds strategic importance for India ... because it is a gateway to energy-rich Central Asian states such as Turkmenistan and Kazakhstan."
A report last year by the Pakistan Policy Working Group, an independent, bipartisan group of American experts on U.S.-Pakistani relations, described Afghanistan as "a new battleground for IndoPakistani hostility."
"Continued Pakistani ambivalence toward the Taliban stems in part from its concern that India is trying to encircle it by gaining influence in Afghanistan," the group said in a report. "Pakistani security officials calculate that the Taliban offers the best chance for countering India's regional influence."
Associated Press Writers Nirmala George in New Delhi and Nahal Toosi in Islamabad contributed to this report.