His words came amid warnings that a Taliban resurgence and factional fighting is crippling rebuilding efforts outside Kabul, while the former ruling militia claimed to be targeting aid workers in Afghanistan.
"We've listened very carefully to the voices of those who've said that bringing security to Kabul alone is not enough," Robertson, NATO's secretary general Robertson said on a brief visit to the Afghan capital.
NATO's governing North Atlantic council "has asked the military to give advice on how or whether we should go beyond Kabul to other parts of Afghanistan."
The NATO chief was in Kabul to visit the 5300-strong International Security Assistance Force (ISAF), which the alliance has been commanding since August.
Afghan leaders, the United Nations and aid agencies have urged repeatedly for the Kabul-confined force to be expanded to the provinces, warning that aid, development and reconstruction were being hampered by violence.
German Chancellor Gerhard Schroeder said Thursday he expected the UN Security Council to agree on ISAF deployment to the provinces "in a very short time."
Robertson said one option was that ISAF could become involved in US-led civil-military teams helping with reconstruction work in the provinces.
ISAF was created under a United Nations mandate in December 2001 to help secure the Afghan capital.
"The options can be to take on the provincial reconstruction teams as ISAF islands, it might be a progressive takeover of the provincial reconstruction teams."
US Defence Secretary Donald Rumsfeld has also voiced support for expansion of ISAF to the provinces.
The NATO chief is on a tour of Central Asia which has already taken him to neighbouring Tajikistan and Uzbekistan.
ISAF was created under a United Nations mandate in December 2001 to help secure the Afghan capital. A separate US-led coalition force of some 12,500 troops is hunting Taliban and al-Qaida remnants across Afghanistan.
Taliban targets aid workers
Meanwhile, the resurgent Taliban movement said on Friday it had killed an Afghan working for a local humanitarian agency and his driver, saying such workers were "American agents" who deserved to die.
Mullah Abdul Samad, an intelligence official in the Taliban regime ousted by US-led forces in 2001, said all aid agencies were involved in propagating Christianity and serving American interests.
Suspected Taliban fighters (C) sit blindfolded after being captured in Zabul province
"All those working in Afghanistan for the interests of America and the Crusaders deserve to be killed," he told Reuters.
Four Taliban guerrillas attacked the vehicle of a worker with the Voluntary Association for Rehabilitation of Afghanistan on Wednesday in southern Helmand province, killing him and injuring his driver.
Haji Mohammad Ayub, a security official in Helmand, said on Friday that the driver died later of his wounds.
"Yes, we have done this," Samad said, speaking by satellite telephone from an undisclosed location.
The attack was the latest on Afghans working for aid agencies in recent weeks, underscoring the need for expanded peacekeeping in the violence-torn country.
Earlier this month, four Afghans working for a Danish aid agency were killed by suspected Taliban rebels in Ghazni province southwest of the capital of Kabul.
"We take responsibility for all the attacks on NGOs (non-governmental organisations) ... who are spoiling the Islamic faith of the Afghan people. They are preaching Christianity and distributing books on Christianity among the people," Samad said.
"(Aid workers) spy on the activities and the hideouts of the Taliban ... they keep contacts with the American forces"
Mullah Abdul Samad,
Taliban intelligence official
Local aid workers were also acting as "informers" for the US-led forces, he said.
"They spy on the activities and the hideouts of the Taliban ... they keep contacts with the American forces."
Assaults on aid workers have spiralled from once a month a year ago, to once every two days, according to the international aid agency CARE.
Relief agencies have warned that without extra security aid and development will be hindered, creating conditions which could result in "growing public support for radical movements." CARE last week said ISAF should be expanded beyond Kabul by year's end.
US soldier injured
A spokesman for the US military, meanwhile, said a soldier was wounded on Thursday night when the vehicle he was travelling in hit a landmine near a US air base at Kandahar in the south of the country.
Colonel Rodney Davis told a briefing that the soldier, who he did not identify by name or nationality, had been taking part in mission to disarm three rockets found near the base. He did not given the condition of the soldier.
The US military also said two rockets had landed near a base of US-led foreign troops and the Afghan National Army at Zormat in Paktia province on Thursday, but caused no casualties.
Davis did not say who might have carried out the attack, but such incidents have been blamed in the past on the Taliban.