An improvised explosive device killed four American service members in southern Afghanistan on Tuesday, the U.S. military said.

U.S. military spokesman Lt. Cmdr. Christine Sidenstricker said the four were killed in the south in an explosion Tuesday. No other information was released pending the notification of family members.

Violence has spiked the last three years, and the U.S. has more than 60,000 forces in the country, a record number.

The rise in American casualties happened the same day that five car bombs detonated simultaneously, rocking Kandahar, Afghanistan's largest southern city, destroying a construction company office and damaging dozens of nearby buildings, officials said. At least 41 people died in the blast and at least 66 were wounded.

The force of the explosion shattered windows around the city and sent flames shooting into the sky.

Afghan officials said the blast appeared to target a Japanese construction company that mostly employs Pakistani engineers. The blast collapsed the company headquarters and destroyed part of a nearby wedding hall, an Associated Press reporter at the scene said.

The AP reporter described the blast as the largest he has heard after almost eight years of living in Kandahar, the site of several large Taliban attacks in recent years.

So many houses and nearby buildings had collapsed that officials feared the death toll could rise further. The AP reporter at the scene estimated that 40 shops had been destroyed.

"Once again they've killed children, women, innocent Afghans. They are not human. They are animals. You can see for yourself the destruction of this enemy," said deputy provincial police chief Mohammad Sher Shah.

Five vehicles filled with explosives detonated together, causing the massive blast, said provincial council member Haji Agha Lalai.

Taliban militants have carried out several complex attacks in Kandahar the last several year. Kandahar is the spiritual home of the Taliban. A large NATO base sits on Kandahar's outskirts, but militants control districts immediately to the city's west.

This year has been the deadliest of the war for U.S. troops. Including the latest deaths, at least 172 American forces have died in the Afghan war this year, according to an Associated Press count.

The U.S. has more than 60,000 troops in the country.