Defeat to Bundesliga leaders Bayern Munich on Saturday may not have been too much of a surprise, but the 1-0 loss meant Dortmund failed to score for the fourth time in five matches across all competitions.
Dortmund face Hoffenheim in the DFB Pokal quarter-finals on Tuesday, and Klopp has challenged his forwards to pose more of a threat in the final third.
"In-scoring areas we lack determination," he said. "It's about standard situations, but also the behaviour around the box.
"We are often 18 metres from goal, but then do not have the ideas to convert.
"We need to be tough and get into promsing positions that make it difficult for teams to defend against."
Two of Klopp's forward players – Marco Reus and Ciro Immobile – have suffered knocks in the lead-up to the Hoffenheim game.
The coach added: "Marco Reus was treated intensively [after the Bayern game], but there should be no problem for Tuesday, nobody has looked worried.
"Ciro Immobile completed a training program on Sunday that would not have been possible on Saturday, but playing a match is something different.
"We will have to wait and see."
