import re


def check_seqs_dic_format(seqs_dic):
    """
    Check sequence dictionary for lowercase-only sequences or sequences
    wich have lowercase nts in between uppercase nts.
    Return suspicious IDs as list or empty list if not hits.
    IDs with lowercase-only sequences.

    >>> seqs_dic = {"id1" : "acguACGU", "id2" : "acgua", "id3" : "acgUUaUcc"}
    >>> check_seqs_dic_format(seqs_dic)
    ['id2', 'id3']
    >>> seqs_dic = {"id1" : "acgAUaa", "id2" : "ACGUACUA"}
    >>> check_seqs_dic_format(seqs_dic)
    []

    """
    assert seqs_dic, "given seqs_dic empty"
    bad_seq_ids = []
    for seq_id in seqs_dic:
        seq = seqs_dic[seq_id]
        if re.search("^[acgtun]+$", seq):
            bad_seq_ids.append(seq_id)
        if re.search("[ACGTUN][acgtun]+[ACGTUN]", seq):
            bad_seq_ids.append(seq_id)
    return bad_seq_ids