KABUL, Afghanistan (CNN) -- Afghanistan is postponing its presidential elections until August 20 due to security and logistical concerns, the country's election commission said Thursday.



Afghan President Hamid Karzai's five-year term is coming to an end this year.



The balloting was originally scheduled for late May, but the independent election commission laid out several reasons for the delay.



Security is a factor, the commission said. It also cited a lack of trained staff, incomplete voter registration and the weather.



It is difficult to campaign or distribute ballots during the rough winter months in the rugged landscape.



The elections are a critical moment for Afghanistan as President Hamid Karzai's five-year term ends. He was elected in December 2004 in largely peaceful polling.



But since then, the Taliban militant movement has regrouped, international troop deaths have increased and there has been an increase in terror attacks, mostly in eastern and southern Afghanistan.



Afghanistan has already registered 3 million voters and is holding voter drives to register more.



The United States will deploy additional troops in coming months to provide much-needed security in the run-up to the election.



The country expects to hold parliamentary elections in 2010.



Meanwhile on Wednesday coalition forces fighting in southern Afghanistan killed four militants, the U.S. military said.



Coalition soldiers were targeting a Taliban leader in the Zabul province when militants fired on them, according to a military statement. Soldiers returned fire, killing the four militants. Soldiers then searched their compound and confiscated several assault rifles.



This operation comes as the U.S. military is contemplating adding three brigades to the war effort in Afghanistan.



Defense Secretary Robert Gates said Tuesday that the troop build up could happen by this summer.



CNN's Atia Abawi contributed to this report
What is the number of registered voters in Afghanistan? How many registered voters are there? Whose term is coming to an end? Who will deploy extra troops? What country will assist with providing security for the elections? How many registered voters are in Afghanistan? What will U.S. troops deploy? How long was Hamid Karzai president for? Whose five year term is ending? Who is ending a five year term? Who has registered 3 million voters?
3 million 3 million Afghan President Hamid Karzai's The United States The United States 3 million provide much-needed security in the run-up to the election. five-year term Afghan President Hamid Karzai's Afghan President Hamid Karzai's Afghanistan
question: What is the number of registered voters in Afghanistan?, answer: 3 million | question: How many registered voters are there?, answer: 3 million | question: Whose term is coming to an end?, answer: Afghan President Hamid Karzai's | question: Who will deploy extra troops?, answer: The United States | question: What country will assist with providing security for the elections?, answer: The United States | question: How many registered voters are in Afghanistan?, answer: 3 million | question: What will U.S. troops deploy?, answer: provide much-needed security in the run-up to the election. | question: How long was Hamid Karzai president for?, answer: five-year term | question: Whose five year term is ending?, answer: Afghan President Hamid Karzai's | question: Who is ending a five year term?, answer: Afghan President Hamid Karzai's | question: Who has registered 3 million voters?, answer: Afghanistan