WASHINGTON (AFP) - At least two local employees of the American consulate in the Pakistani city of Peshawar have been killed in an explosion while out on an anti-narcotics mission, United States Secretary of State John Kerry said on Tuesday.

The top American diplomat said several Pakistani soldiers also died in the blast involving an improvised explosive device (IED).

"Just this morning I woke to the news that we have lost two local employees in Peshawar who worked with our consulate there who were going out on an effort to eradicate narcotics fields," Kerry said at an event.

"An IED exploded and several were lost. A few of the soldiers who were there to guard them also," he added, without going into more specifics.

The State Department subsequently said the two Pakistani employees of the US Mission in Pakistan were killed earlier on Tuesday in an attack on a Pakistani government anti-narcotics force convoy in an area of the country's vast tribal zones that border Afghanistan.

"The US government strongly condemns the attack," spokesman John Kirby said.

"Pakistan has suffered greatly at the hands of terrorists and violent extremists," he added. "The United States stands in solidarity with the people of Pakistan and all who fight the scourge of terrorism."

News of the deaths comes after Kerry welcomed Pakistani foreign affairs adviser Sartaj Aziz to the State Department on Monday for talks on the "strategic" partnership between their two countries centred on cooperation in the anti-terror fight.

Peshawar, located in northwest Pakistan, made sombre global headlines in Dec 2014 when the Taleban attacked a school there, massacring some 150 people, mostly children, prompting the country's army to intensify its offensive against Islamist militants.