Roadside bombs killed four NATO troops in Afghanistan, the international force said on Saturday, adding to a violent summer as coalition forces step up patrols in the Taliban—dominated south.

Separately, NATO reported that Afghan and foreign troops found nearly 2 tons (1.8 metric tons) of processed heroin, 1,800 pounds (800 kilograms) of opium and 200 pounds (90 kilograms) of ammonium nitrate on Friday that could have been used to make 25 roadside bombs in the southern province of Helmand.

The drugs had a street value in the United States of more than $38 million before taking into account the common practice of cutting them with other ingredients, which would exponentially increase the value, according to the U.S. Drug Enforcement Agency.

Another joint force arrested a Taliban insurgent involved in bomb—making after intelligence indicated he was plotting an attack during the upcoming international conference on Tuesday in Kabul, NATO said. Several other insurgents were arrested during the raid on Friday night in Kabul.

An American service member was killed by a blast in eastern Afghanistan on Saturday, while another coalition soldier, whose nationality was not released, died in a roadside bomb in a southern province, NATO said. It gave no other details.

Two members of the multinational force died in a single explosion on Friday in the south. The NATO—led force gave no details but said one of the troops killed was American.

Roadside bombs planted by insurgents are one of the leading killers of both international troops and civilians in Afghanistan.

To counter the threat, the U.S. is sending $3 billion worth of detection equipment and bomb—resistant vehicles to Afghanistan, the Defence Department said earlier this month. The equipment includes tethered surveillance blimps to give troops a bird’s eye view of certain areas, plus unmanned surveillance planes and Mine Resistant Ambush Protected vehicles.

Last month was the deadliest of the nearly nine—year—old war for international troops, with 103 killed. So far in July, 52 international troops have died, 39 of them American.

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