The current invention provides oligonucleotides which comprise a dinucleotide consisting of a 5' locked nucleic acid (LNA), a phosphorothioate internucleoside linkage bond to a 3' RNA or RNA analogue. The dinucleotide reduces the strength of hybridization of the oligonucleotide to a complementary nucleic acid target. The modification can be used to modulate hybridisation properties in both single stranded oligonucleotides and in double stranded siRNA complexes, particularly in oligonucleotides where the use of LNA results in excessively strong hybridisation properties.