US election observers warned Nigeria on Sunday that next week's presidential elections could be undermined if the shortcomings of this weekend's parliamentary poll are repeated. The International Republican Institute (IRI), in a statement released here, said that it commended the Nigerian people for turning out to vote in largely peaceful legislative elections on Saturday. But the group, which dispatched 20 poll monitors to Africa's largest ever election, said it had witnessed "serious lapses at critical levels of the election administrative structure".