Kabul, Afghanistan (CNN) -- Afghanistan President Hamid Karzai issued a decree Tuesday disbanding all private security firms within four months.
The decree involves international and national private security companies. The security employees of those companies will be eligible to join the Afghan National Police and may bring their weapons.
"In order to protect Afghan life and property, avoid corruption, security irregularities and the misuse of military weapons, ammunition and uniforms by the private security companies which have caused tragic incidents, and after the required assessment, I approve shutting down all private security companies within four months, including both domestic and foreign," the decree said.
"Employees of private security companies who wish to, and are eligible, can join the ANP with their weapons and ammunition or without," it added. "After they register with the ANP, the Ministry of Interior must commence the process of shutting down private security companies."
In Washington, Pentagon spokesman Bryan Whitman called the four-month timeline set by Karzai "very challenging."
Whitman said the Pentagon and Afghan government share the goal of eliminating all private security contractors, but he questioned whether it could happen so quickly.
"We recognize that Afghanistan still presents a daunting security challenge," Whitman said. "We want to achieve this goal (of no contractors) in a deliberate way, that recognizes the scope and scale of that security challenge."
There are roughly 26,000 workers under U.S. contract in Afghanistan, with 19,000 of them employed under Defense Department contracts. In total, there are 37 approved, licensed companies, and the Pentagon says 17 of those are Afghan-owned.
Karzai's decree also said that ammunition belonging to private security companies but registered with the Ministry of the Interior should be transferred to Afghanistan's government.
"According to signed contracts between these security companies and the Ministry of the Interior, the Ministry of Defense, and the National Directorate of Security, these agencies can buy these munitions from these companies with their compliance and consent," the decrees said. "In addition, the Afghan visas for their international staff shall be terminated."
The move spotlights the issue of the role and conduct of U.S. security contractors, who protect embassies and companies, perform training and help convoys move through dangerous areas. Violent incidents involving such contractors have enraged Afghans.
On Monday, U.S. State Department spokesman P.J. Crowley told reporters that U.S. officials would study the expected decree from Karzai.
"Well, at this moment, we believe that there is still a need for private security companies to continue to operate in Afghanistan," Crowley said. "We certainly agree that over time this responsibility should transition to the government of Afghanistan. I think we have a shared goal of improving oversight and management."
International Security Assistance Force spokesman Brig. Gen. Josef Blotz told reporters at a briefing last week that the force "welcomes the initiative."
"Binding rules and guidelines for employment by private security companies are needed," he said.
Blotz said the force has been aware of problems in the private security business "for years" and that coordination is needed among the force, the Afghan government and the international community.
He said the NATO-led force had started looking into the issue last year and had some recommendations, including the need for all companies to be registered and put under government oversight and legal control. He also said there is a problem with companies that subcontract their work out.
The decree comes after an incident in July, when a vehicle carrying contractors from DynCorp International were involved in an accident that resulted in Afghan casualties.
On Tuesday, two security contractors charged with fatally shooting two Afghan men after a traffic incident will be arraigned in a Virginia courtroom.
Christopher Drotleff and Justin Cannon worked as security contractors for a subsidiary of Xe, the military contracting firm formerly known as Blackwater Worldwide. They are each charged with two counts of second-degree murder and one count of attempted murder in connection with the May 2009 shooting in Kabul, Afghanistan.
Both men were in Afghanistan working for the security company Paravant -- a subsidiary of Xe -- to help the U.S. Army train Afghan troops.
Drotleff, Cannon and two other contractors were driving with interpreters on a busy Kabul street called Jalalabad Road when a car slammed into one of their two vehicles, they said.
The contractors said they fired at the oncoming vehicle in self-defense.
A similar issue arose in Iraq after a September 2007 confrontation involving then-Blackwater contractors that left 17 Iraqi civilians dead.
Blackwater lost its contract there after Iraq's government refused to renew its operating license. The company then changed its name to Xe, and it continues to receive multimillion-dollar contracts in Afghanistan.
CNN's Chris Lawrence contributed to this story.