The latest deaths brought to at least 30 the number of American service members who have died in Afghanistan this month two more than the figure for all of June 2008, which had been the deadliest month for the U.S. since the 2001 U.S.-led invasion drove the Taliban from power.
July's death toll for the entire U.S.-led coalition, which includes American, British, Canadian and other forces, stands at 55 well over the previous record of 46 deaths suffered in June and August of 2008.
U.S. commanders had predicted a bloody summer after President Obama ordered 21,000 additional U.S. troops to Afghanistan in a bid to turn the tide against a resurgent Taliban and shift the focus on the global war against Islamic extremism from Iraq.
Meanwhile, friends and family of an American soldier who was captured in Afghanistan Sunday, shaken by the image of the frightened young private in a Taliban video posted online.
Pfc. Bowe R. Bergdahl, 23, was serving with an Alaska-based infantry regiment earlier this month when he vanished, just five months after arriving in Afghanistan. He was serving at a base near the border with Pakistan in an area known to be a Taliban stronghold.
NATO's outgoing Secretary-General Jaap De Hoop Sheffer said Monday that terrorism would spread through the world if NATO forces fail in Afghanistan.
"Al Qaeda would have a free run again, and their terrorist ambitions are global," he said in a speech at London's Chatham House think tank. "Those who argue otherwise who say we can defend against terrorism from home are simply burying their heads in the sand."
Defense Secretary Robert Gates has warned that U.S.-led forces must demonstrate progress in Afghanistan by next summer or face a public perception that the conflict cannot be won. Heavy losses this month have already triggered a public debate in Britain that the war in Afghanistan may not be worth the price.
With more troops in the country, American and British forces have been striking deeper into Taliban strongholds in the south, hoping to establish enough security for Afghans to choose a president next month and cut insurgent supply lines into Pakistan.
British military authorities said Monday that bombing attacks in southern Afghanistan soared nearly 43 percent for the first five months of this year over the same period last year.
U.S. troops have also stepped up efforts in eastern Afghanistan to curb the movement of militants to and from safe havens in Pakistan's lawless tribal region.
A NATO statement said the four soldiers were killed by an improvised explosive device in the east of the country but gave no further details. A U.S. spokesman, Lt. Robert Carr, confirmed all four were Americans.
Also Monday, the British Ministry of Defense announced that a British soldier was killed the day before by a roadside bomb during a foot patrol in Helmand province.
Roadside bombs now account for more than two-thirds of all casualties among the international force as the Taliban demonstrate greater skill in manufacturing and planting the explosives. Bombings rose by 25 percent in the first four months of 2009 over the same period last year, and the U.S. command expects them to increase 50 percent this year to 5,700 up from 3,800 last year.
The increased threat from roadside bombs and Afghanistan's formidable terrain of high mountains and deserts have forced the international military force to rely heavily on aircraft to transport personnel and supplies around the country. The increased tempo of the conflict has strained air assets and may have been behind a series of aircraft accidents in recent weeks.
In the latest mishap, a British Tornado GR4 fighter jet crashed Monday on takeoff inside the Kandahar Airfield, but the two crewmen managed to eject safely, according to a NATO spokesman Capt. Ruben Hoornveld. British officials said the crash was not a result of hostile fire but the cause was still under investigation.
The crash occurred one day after a Russian-owned civilian Mi-8 helicopter slammed into the tarmac at the same base shortly after takeoff, killing 16 people on board. Two Americans died Saturday when their U.S. Air Force F-15E Strike Eagle fighter jet crashed in central Afghanistan.
A U.S. helicopter made a "hard landing" the same day, injuring several soldiers. U.S. officials said neither incident was due to hostile fire.
Taliban militants shot down a Moldovan-owned Mi-6 transport helicopter last week in southern Afghanistan, killing six Ukrainian civilians on board and an Afghan child on the ground.
Earlier in July, two Canadian soldiers and one British trooper were killed in a helicopter crash in Zabul province. Officials said the crash did not appear to be caused by Taliban fire.
Also Monday, officials reported that at least a dozen Afghan civilians had been killed in violent incidents.
In the northern province of Kunduz on Sunday, German soldiers fired on a pickup truck approaching at high speed and suspected of carrying Taliban fighters. Provincial Gov. Mohammad Omar said three civilians were killed, but German authorities said one died.
Defense Ministry spokesman Christian Dienst said in Berlin that the driver ignored warning shots before troops fired at the vehicle's engine to disable it. Three Afghans were injured and a fourth fled, Dienst said.
Prosecutors in Potsdam, where the German military's mission command center is headquartered, said they were examining evidence to determine whether to open a criminal investigation.
In the western province of Farah, a van full of civilians struck a roadside bomb Sunday, killing 11 people on board, including a child and his mother, said Mohammad Younis Rasouli, the deputy governor. The bomb was probably intended for Afghan or international troops.