Increased interactions between dissolved ions and partial charge centres on the water molecule.
I assume you mean common salt (sodium chloride). Dissolving this in water yields aqueous solvated sodium and chlorine ions. Water molecules are highly polar with partial positive charges on the hydrogen atoms and partial negative charges on the oxygen atoms. When solvated sodium ions form interactions with the partial negative charged oxygen atoms in water, and similarly chlorine (chloride) ions form interactions with the partially positive charged hydrogen atoms in water.
Whilst this does to an extent interefere with hydrogen bond formations between water molecules, overall (and depending on the concentration of dissolved salt) the net effect is an increase in interactions that tends to increase surface tension.