The detention of an Indian border guard by Pakistani forces has injected another element of tension into the already volatile confrontation between the two countries after last week’s deadly terrorist attack in Kashmir.

The family of the Indian border guard, Purnam Kumar Shaw, who is part of the paramilitary Border Security Force, has expressed concern about his fate.

He was accompanying farmers looking after their crops along the border in the Indian state of Punjab when he strayed across the line demarcating Indian and Pakistani territory and was detained, according to the Indian news media.

He was detained on Wednesday, a day after the terrorist attack in the Indian part of Kashmir, which killed 26 civilians and has pushed the nuclear-armed neighbors to the verge of military confrontation.

India has accused Pakistan of having a hand in the attack and has indicated it is preparing a military strike, in addition to other punishing measures it has already laid out. Pakistan has denied the accusations and reciprocated with its own retaliatory measures.

Mr. Shaw’s detention could give the Pakistani government a bargaining chip and affect India’s options for striking Pakistan.