39 killed in blast at security checkpoint in northwestern Punjab province . Explosion occurs in Swat Valley in the volatile Swat Valley . Intercepted phone call tipped officials to Monday 's attack , general says . Mingora has been scene of clashes with Taliban militants .
41 killed in blast at security checkpoint in northwestern Pakistan . Explosion occurs in the Shangla district in the volatile Swat Valley . Intercepted phone call tipped officials to Saturday 's attack , general says . Swat Valley has been scene of clashes with Taliban militants .