Port Harcourt - Unknown gunmen stormed and bombed the site of a planned opposition rally outside southern Nigeria's oil city of Port Harcourt early on Saturday, though police said no lives were lost.
Rivers state police commissioner Dan Bature said the incident in Okrika occurred around 04:30 (03:30 GMT), long before the start of the rally by the All Progressives Congress (APC) for its governorship candidate in the 28 February election.
He said the attackers invaded the venue with an explosive device and drove away workers preparing for the event.
Bature advised the APC to postpone the rally in the interest of peace.
Tempers have been rising ahead of next month's presidential, parliamentary and governorship vote in Africa's most populous country, with smear speeches dominating campaigns.
The APC has blamed President Goodluck Jonathan's ruling People's Democratic Party for the series of violent attacks unleashed on its supporters, facilities and offices since the start of campaigns last month.
National police chief Suleiman Abba on Saturday warned politicians against inciting violence in the run up to the elections.
"The IGP (Inspector General of Police) notes that it is particularly worrisome that, of (late), thugs and miscreants have been employed by some political parties to disrupt and truncate the political campaigns of their opponents," his office said in a statement, vowing to punish trouble makers with the full force of the law.
Electoral violence has blighted past polls since Nigeria's independence from Britain in 1960, and there have been warnings that there could be a repeat of clashes in 2011, which left hundreds dead.
Jonathan is seeking a second, four-year term and faces former military ruler Muhammadu Buhari, the APC candidate, in the 14 February election.
