(CBS)  Vice President Abdul Qadir was buried Sunday with full military honors one day after he was gunned down in an attack that Afghans fear may bring new instability to a nation struggling to build peace after decades of war.

An estimated 10,000 people followed Qadir's body, carried on a gun-carriage, as it moved from the city's White Mosque to the grave in the lush Amir Shaheed Gardens in the city center. Afghan troops in full uniform marched in the procession.

As the body, wrapped in a green, red and black Afghan flag, was lowered into the grave, a Pashto-language poem read over a loudspeaker hailed Qadir as "a unique man" and "a hero of Afghanistan." Seven shots were fired into the air, and male mourners wept only and chanted his name.

Qadir, who also served as minister of public works and governor of Nangarhar province, died Saturday in a hail of bullets after two gunmen opened fire on his vehicle as it was leaving his office in Kabul. His driver, who was also a son-in-law, was killed too but the gunmen escaped.

CBS News correspondent Elizabeth Palmer says the government's challenge now is not only to catch the killers, but to make sure the assassination doesn't spark a new round of ethnic violence and war.

Afghan President Hamid Karzai will call for foreign help in cracking the case if local authorities are unable to make progress in their own investigation, Afghan television reported Sunday.

"If our investigation team fails because of the lack of professional skills and equipment, we will ask foreign friends and international organizations for help," Karzai was quoted as saying by the state-run Afghan television.

The TV report said two men had been detained for questioning after they were stopped at a Kabul checkpoint in a car similar to the one used by the killers for their getaway.

Ten guards on duty at the Ministry of Works in front of which Qadir was killed were arrested on Saturday because they failed to react properly, according to Kabul police chief Din Mohammed Jurat.

Qadir's body was flown here to the Nangarhar capital from Kabul aboard a helicopter provided by the international peacekeeping force following a prayer service attended by Karzai and thousands of mourners.

No group claimed responsibility for the attack. Turkish Army Col. Samet Oz, spokesman for the 5,000-strong international peacekeeping force in Kabul, described the killing as "an individual attack designed to destabilize the transitional government."

Qadir was the most prominent ethnic Pashtun in the government after Karzai himself, and his assassination threatens to stir unrest here in Nangarhar province, a relatively wealthy trading and opium poppy-growing region that borders Pakistan.

"Qadir was a martyr who cannot be replaced," Karzai was quoted as saying. "He was not only my minister but also my best friend."

"He was a champion of the Holy War and during the fight against the Taliban and he will remain a part of the Afghanistan history," Karzai said.

Instability in such a key region could complicate efforts by the Karzai government to extend its authority beyond Kabul. Qadir was appointed as one of five vice presidents during last month's Afghan grand council, or loya jirga, to bring ethnic balance into a government which had been dominated by ethnic Tajiks.

In Washington, U.S. lawmakers said Qadir's assassination should compel the United States to consider an active role in providing security in the country. U.S. operations have been directed at pursuing Taliban and al Qaeda fugitives rather than peacekeeping.

"This was definitely a throwback to the old Afghanistan and a setback to the establishment of the new Afghanistan," said Sen. Bob Graham, chairman of the Senate Intelligence Committee, on NBC's "Meet the Press."

Sen. Chuck Hagel, who serves on the Senate Foreign Relations Committee, said he feared that "we may see this government and our efforts unwind here if we don't make the appropriate investment of men and effort and resources."

During a speech to the mourners, Afghan Chief Justice Fazle Hadi Shinwari promised the government was doing everything possible to find the killers and he urged people to remain calm.

"This is a test for the people of Afghanistan, of Nangarhar," Shinwari told mourners here. "They should be aware of this and pass this test."

Throughout the day, armed police manned checkpoints on all approaches to Jalalabad and roamed the largely deserted streets. Most merchants closed their stores for the funeral although Sunday is a business day.