By Pam O'Toole
BBC Central Asia analyst
Two aid workers from the Afghan Red Crescent Society have been killed and three others injured in an ambush south-west of the capital, Kabul
Afghanistan is awash with weapons, including tanks
In a separate incident, the United Nations refugee agency, UNHCR, announced that it was suspending operations in Kunar Province in eastern Afghanistan after a rocket was fired near one of its compounds.
The UN and a number of other aid agencies had already suspended activities in parts of southern Afghanistan following a flurry of attacks in those areas.
The latest incidents come amid a deteriorating security situation and followed one of the bloodiest days in Afghanistan in the past year.
Some 60 people were killed in violent incidents on Wednesday.
These included an explosion on a bus which Kabul blamed on the Taleban, a battle between Afghan Government forces and suspected Taleban and al-Qaeda elements, and factional fighting.
There are a variety of reasons behind the current escalation in violence.
Persistent poverty, easy access to weapons, and slow progress in building a national Afghan security force have fuelled banditry.
There is continued fighting among rival warlords, and the Kabul government has yet to extend its authority across the country.
And finally, there is the re-emergence of the Taleban. They began reappearing from hiding earlier this year, calling on Afghans to expel what they described as foreign crusaders.
Their claims to be regrouping were borne out by an increasing number of attacks against Western troops, Afghan Government forces, clerics regarded as loyal to the Kabul government, and foreign aid workers.
Most of these attacks have been in the largely Pashtun south and south-east of the country. In their old stronghold of Kandahar, the Taleban are said to be operating in an increasingly open manner.
In other areas, it is alleged they are slipping across the border from Pakistan - although Islamabad denies harbouring Taleban militants.
Warlord wings clipped
Human Rights Watch recently warned that a climate of fear in Afghanistan was threatening efforts to adopt a new constitution and to hold national elections next year.
Warlord Ismail Khan has lost his military command
Efforts are underway to improve the situation, although they are unlikely to produce immediate results.
On Wednesday, the UN's special envoy for Afghanistan, Lakhdar Brahimi, again called on the UN Security Council to expand the international peacekeeping force in Kabul to other areas of the country.
Meanwhile, the Kabul government is accelerating plans to train a national police force.
And President Karzai has announced a variety of measures in a bid to rein in powerful governors and warlords and try to extend Kabul's control to areas outside the capital.
In a reshuffle of officials on Wednesday, he replaced the governors of two restive provinces where the Taleban are said to be particularly active.
He simultaneously stripped the powerful governor of the western province of Herat, Ismail Khan, of his additional position as military commander.