"We don't want to be seen as a country which is reluctant to lend full support to any of its neighbors facing security problems," he told reporters.
Najib was commenting on a series of bombings in southern Thailand, the most recent being last Saturday, which injured seven Malaysians at a pub behind a hotel near the border with Malaysia.
Najib, who is also the defense minister, said Malaysian authorities had some leads on the group involved in the bombing and police were still investigating.
But he rejected Thaksin's statement that the bombers had escaped into Malaysia.
"We don't harbor terrorist or make our country a terrorist haven," he said.