A roadside bomb killed two Polish soldiers patrolling in eastern Afghanistan, officials said Wednesday, while NATO announced the seizure of $400 million in opium in the south.

The explosion hit the troops in the Sharan district of Paktika province on Tuesday, said NATO's International Security Assistance Force.

The Polish troops were returning from a humanitarian aid meeting in a village when their Humvee drove over a roadside mine, Maj. Dariusz Kacperczyk, spokesman for the Polish army operational command, said in Warsaw.

The two soldiers killed were identified as Cpl. Szymon Slowik and Pvt. Hubert Kowalewski. One soldier was also wounded. Poland has about 1,200 troops in Afghanistan.

The latest deaths bring the number of foreign troops killed in Afghanistan to 21 this year, according to an Associated Press tally of figures from ISAF and the U.S.-led coalition.

In 2007, insurgency-related violence killed more than 6,500 people, including 222 foreign troops. Last year was the deadliest yet since the U.S.-led invasion in 2001.

Paktika borders Pakistan's lawless tribal region, which is used by militants as a base to plan and launch attacks inside Afghanistan.

Despite the latest deaths, U.S. military officials insisted Wednesday the province has made great strides since the deployment of foreign troops. The government has extended its reach into areas that had no government presence before, roads have been built and more children are going to school, officials said.

"When we arrived in 2005 there was not one kilometer of road in Paktika province," said Lt. Col. Michael Fenzel, a U.S. military commander. "Now we have over 300 kilometers of road, and they are opening up commerce between ... districts."

NATO and Afghan soldiers, meanwhile, discovered and destroyed a massive opium haul during a patrol last week in the Sangin district of southern Helmand province, ISAF said in a statement issued late Tuesday.

The troops found 1.65 tons of opium — which ISAF said was worth $400 million — and a "significant quantity" of drug-making equipment last Thursday, it said. The $400 million figure appeared to be the opium's estimated street value once it was trafficked outside Afghanistan.

Helmand, the front line of the bloodiest battles in recent years between militants and foreign forces, is the world's largest opium-producing region.

Officials estimate that up to 40 percent of proceeds from Afghanistan's drug trade — an amount worth tens of millions of dollars — is used to fund the insurgency.

In other violence, a remote-controlled bomb hit a civilian vehicle Wednesday in eastern Khost province, killing the driver and wounding six people, said Khost public health chief Dr. Mohammadin Mohammadi.

A rocket attack on an Afghan National Army patrol killed two soldiers and wounded six others Tuesday in the Maiwand district of southern Kandahar province, the Ministry of Defense said in a statement.

Seven insurgents were killed in two separate clashes in Helmand on Monday, the ministry statement said.

A rocket fired by insurgents in the Kajaki region of Helmand province killed five Afghan civilians on Monday, the U.S.-led coalition said.