Read the latest on what's happening on the ground in Afghanistan in the Afghanistan Crossroads blog.
Kabul, Afghanistan (CNN) -- German Chancellor Angela Merkel paid a visit to Afghanistan on Saturday, two days after Germany's top diplomat announced a planned reduction in troop levels and a day after one of its soldiers died.
The visit also comes on a violent day across the country, where two coalition soldiers died in combat, two civilians were killed in a bombing, and 20 insurgents died in fighting. NATO's International Security Assistance Force also released initial results of a probe into a friendly fire incident that left four Afghan soldiers dead.
Merkel arrived in Kunduz in northern Afghanistan to visit German troops, a German government spokesman said. The spokesman would not give any further details except to say the trip was previously unannounced for security reasons.
Germany has more than 4,800 troops serving with ISAF.
Germany will begin reducing its troop levels in Afghanistan in late 2011, Foreign Minister Guido Westerwelle said in a speech to German parliament Thursday.
Northern Afghanistan, which is typically not as volatile as the eastern and southern regions of the country, has seen an uptick in violence recently.
And, an ISAF official confirmed to CNN that a 21-year-old German soldier was killed Friday in a non-battle related injury in Pol-e-Khomri, located in northern Afghanistan's Baghlan province.
That brings the number of German military deaths in the Afghan war to 45.
Meanwhile Saturday, violence raged in Afghanistan:
Two coalition service members died, one after an insurgent attack in the east and another after an IED strike in the south, NATO's International Security Assistance Force said.
With the latest attacks Saturday, the number of coalition deaths has risen to 700 this year, according to a CNN tally.
In Kapisa province, more than 20 insurgents were killed, including several Taliban sub-leaders, by coalition forces during a fight in eastern Afghanistan. Insurgents fired at a patrol and the troops returned fire and brought in air support.
In Kandahar province, a car bomb killed two civilians, including one child, and wounded 11 children.
ISAF and Afghan officials on Saturday released an initial assessment of how a deadly friendly fire incident occurred on Wednesday in Helmand province.
Four Afghan National Army service members were accidentally killed in an ISAF air strike.
ISAF troops saw "small arms fire impacting close to their location" and assumed they were under fire, an ISAF statement said.
"Not wanting to give away their position since they were conducting an operation, ISAF service members called in air support" and killed the four -- all wearing Afghan uniforms.
The assessment team couldn't determine why the Afghan troops were "firing their weapons and why they didn't know coalition forces were operating in the area."
"This is a regrettable tragedy that should not have happened, our thoughts and concerns are with the victims' families," said U.S. Air Force Brig. Gen. Tim Zadalis, an ISAF spokesman.
The fighting reflects the tough fight underscored in a U.S. review of operations in Afghanistan and Pakistan.
At a press conference in Kabul on Friday, Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said the review "shows us that we are on the right track," but more progress needs to be made, particularly in the area of government and the rule of law.
"I remain convinced that we have the right strategy, we have the right leadership and we now have the right resources in place to disrupt, dismantle and defeat al Qaeda, to reverse the momentum of the Taliban and to prevent Afghanistan from becoming a safe haven," Mullen said.
CNN's Matiullah Mati, Frederik Pleitgen, Katy Byron and Joe Sterling contributed to this report.