Germany saw about 890,000 asylum-seekers arrive last year, many after Ms Merkel decided in September 2015 to let in migrants who were stuck in Hungary.
Numbers have since declined sharply, but Ms Merkel’s approach to the migrant crisis has provoked discord within her Christian Democratic Union party, which has seen a string of poor state election results this year.
“A situation like the one in the late summer of 2015 cannot, should not and must not be repeated,” Ms Merkel told party delegates at a congress in the western city of Essen.
“That was and is our, and my, declared political aim,” she said. Ms Merkel’s government has moved to declare several countries “safe” - meaning people from there cannot expect to get refuge in Germany.