KABUL, Afghanistan — Terrorists killed 17 road workers in Afghanistan’s lawless south yesterday, part of a spike in violence that left 40 people dead in two days.

Sixteen other construction workers were wounded in the attack in Zabul’s Shinkay district, Interior Ministry spokesman Zemeri Bashary said. Afghan and international security forces responding to the ambush killed seven terrorists and wounded 12, he said.

Road-building is a key part of Afghan reconstruction and many projects are in remote, insurgency-plagued areas. Terrorists have targeted work crews in roadside bomb attacks, ambushes, and kidnappings. In January, terrorists in eastern Nuristan province beheaded four road construction workers.

The 40-nation military alliance in Afghanistan has stepped up efforts to contain the growing insurgency and America now has some 32,000 troops in the country, the most since the 2001 American-led invasion. Last year was the deadliest since the invasion, with more than 8,000 people killed, mostly terrorists, the United Nations says.

Democrats in the Senate have warned the Bush administration that Washington hasn’t committed enough troops or aid money to Afghanistan, even as it poured resources into Iraq.

“The negligent policies of the last half-decade have permitted Al Qaeda and the Taliban to regenerate and to pose a greater threat to the national security of the United States than at any point since Sept. 11, 2001,” the letter, which was dated Sunday, said.

Afghanistan has become a virtual narco-state where drug-fueled corruption and warlords are “recreating the chaos that enabled the Taliban to seize power in the 1990s,” the Democrats wrote. Forty-six senators signed on, including the Senate majority leader, Harry Reid, and presidential candidates Hillary Clinton and Barack Obama.