Four Frontier Corps (FC) soldiers were martyred while six others were injured after terrorists ambushed them during a fencing activity at the Pakistan-Afghanistan border, the military's media wing said in a statement on Wednesday.

The Inter-Services Public Relations (ISPR) said that the troops were moving for fencing activity along the border in the Manzakai sector in Balochistan's Zhob when "terrorists from Afghanistan ambushed" them.

FC troops responded to the attack promptly, it said.

The injured soldiers were evacuated to the Combined Military Hospital (CMH) Quetta, the ISPR added.

The martyred soldiers include Havaldar Noor Zaman, Sepoy Shakeel Abbas, Sepoy Ehsan Ullah, and Naik Sultan.

The Foreign Office (FO), in a statement issued later in the day, said that around 20 terrorists were involved in the attack and they used small arms and heavy weapons.

"Pakistan strongly condemns such organised attacks and considers these detrimental to ongoing peace and stability along Pakistan-Afghanistan border," the statement quoted FO spokesperson Zahid Hafeez Chaudhri as saying.

It added that the Afghanistan embassy had been asked to convey Pakistan's concerns to the relevant authorities in the country to "undertake effective measures against organised groups of terrorists operating from Afghan soil, follow mutually agreed protocols and SOPs and avoid recurrence of such incidents in future".

Interior Minister Sheikh Rashid condemned the attack, terming it "very saddening".

"Terrorists cannot dampen the courage of Pakistan's forces. Fencing work at the Pakistan-Afghanistan border will be completed under any condition," he emphasised in a tweet.

Leader of the Opposition in the National Assembly Shehbaz Sharif also strongly condemned the "cowardly attack".

"Our brave FC soldiers laid down their lives today while defending the motherland at Pak-Afghan border ... [I] send my heartfelt condolences to the families who lost their loved ones. Prayers for the quick recovery of the injured," he tweeted.

In October of last year, a soldier was martyred and another wounded when terrorists fired gunshots from across the Pak-Afghan border on the Pakistan Army post in Bajaur. Another such attack had taken place a month earlier in which a soldier was martyred as well.

After the September attack, the ISPR director general had said that the issue of border management had been raised with Afghan authorities multiple times to prevent the use of the neighbouring country's soil for attacks against Pakistan.

Additional reporting by Naveed Siddiqui.