LONDON (AP) — The London Stock Exchange has delayed the opening on some its biggest companies saying it has a "trading services issue."

Trading in companies in the exchange's FTSE100 and FTSE250 indexes, was due to open at 8 a.m. (0700 GMT; 3 a.m. EDT) on Friday, but did not.

Smaller companies were trading as normal.

It gave no further details and says it will provide updates as soon as it has any further information.

The last time there was a significant delay to the opening of the exchange was in June last year, when it opened an hour later than normal because of a software issue.