UPDATE 2-ECOWAS suspends Niger, says election invalid

* Authorities say poll calm; no turnout figures

* President Tandja seen tightening grip on power

* ECOWAS suspends Niger, says will not recognise result

(Updates with reaction to ECOWAS suspension)

By Abdoulaye Massalatchi

NIAMEY, Oct 20 (Reuters) - West Africa's regional bloc on Tuesday suspended Niger in protest against what it said were flawed parliamentary elections being held there.

The Economic Community of West African States (ECOWAS) said it would not recognise the result of the vote, which is expected to allow President Mamadou Tandja to tighten his grip on power and deepen the uranium-mining country's constitutional crisis.

"The holding of the elections is a clear move by the authorities in Niger to further entrench the constitutional illegality currently prevailing in the country," said a spokesman for Nigerian President Umaru Yar'Adua, who is ECOWAS chairman.

Turnout for the election was patchy after the opposition called for a boycott of the poll.