LOME - Nine Togolese politicians who were running a campaign against a new constitution that could allow President Faure Gnassingbe to extend his 19-year rule have been arrested, a spokesperson for an opposition coalition said on Thursday.

Opposition voices are growing in the tiny phosphate-producing West African nation over constitutional reform that could change the way the president is elected.

Some members of the opposition coalition were detained on Wednesday afternoon while they were campaigning against the constitution at a market in the suburbs of Togolese capital Lome, spokesperson Thomas Nsoukpoe said.

Others were detained at night during a meeting at the house of a coalition member.

Togo's opposition parties started their campaign after the national assembly adopted the new constitution that lengthens presidential terms by one year to 6 from 5 while limiting the number of terms to one.

Under the new constitution, which introduces a parliamentary system of government, the president will no longer be elected by universal suffrage, but by members of parliament.

The constitution does not take into account the time already spent in office, which could enable Faure Gnassingbe to stay in power until 2031 if he is re-elected in 2025.

In reaction to opposition voices, the president's office on Wednesday announced nationwide consultations on the revision of the constitution, and delayed parliamentary and regional elections initially scheduled for April 20.

Several parties condemned this decision and called for demonstrations on April 11, 12 and 13.

"As the electorate has been convened by decree, it is not possible to suspend the electoral campaign and postpone the elections by means of a simple announcement," they said in a statement on Thursday.

The presidency did not immediately reply to Reuters requests for comment on the arrests made on Wednesday.

(Reporting by Alice Lawson; Writing by Anait Miridzhanian; Editing by Sandra Maler)