* Ivorian troops reportedly attacked Yopougon church
* U.N. seeking clarity on report of mass grave
* Gbagbo lawyers turned away at airport
ABIDJAN/GENEVA, May 6 (Reuters) - The United Nations is investigating alleged abuses committed by Ivorian soldiers during clashes with militiamen in Abidjan this week, the world body&${esc.hash}39;s human rights office said on Friday.
The probe could add pressure on new President Alassane Ouattara, whose forces are already accused of rape, looting and executions during an offensive in March and April to oust former leader Laurent Gbagbo.
"Our staff in Cote d&${esc.hash}39;Ivoire are investigating reports of human rights violations in Yopougon district of Abidjan committed allegedly by both the FRCI (Ivorian army) and the pro-Gbago militiamen who have been holding out in that district," U.N. human rights spokesman Rupert Colville told a news briefing in Geneva.
"They are particularly looking at an attack against a Baptist church allegedly by FRCI forces earlier in the week," he said, without giving further details.
Colville said U.N. staff were also investigating reports of a mass grave in the district, where pro-Gbagbo gunmen have made a last stand after Gbagbo was arrested in mid-April.
A spokesman for Ivory Coast&${esc.hash}39;s military said on Thursday that its soldiers had recaptured a naval base from the remnants of the militia, leaving them no place from which to launch attacks, and eliminating the last major pocket of resistance.
The Red Cross said this week its staff had recovered dozens of corpses from Yopougon from recent and old fighting there, and had also discovered a field in which residents said many as 30 bodies had been buried.
The U.N. could not say if this was the mass grave.
Gbagbo, who had led the country since 2000, refused to step down after a November 2010 election he was judged to have lost, triggering all-out conflict that killed thousands and displaced more than a million people.
Ouattara has launched an investigation into Gbagbo and his inner circle for alleged human rights abuses during the conflict, which tore open the wounds of a 2002-2003 civil war -- even as his own forces, a ragtag collection fo former rebels, have been accused by rights groups of their own abuses.
Three Paris-based lawyers representing Gbagbo said they sought to enter Ivory Coast on Friday to attend Gbagbo&${esc.hash}39;s scheduled hearing in the northern town of Korhogo but had been forced to return to France when two of them had their visas refused at Abidjan airport.
"The three lawyers were turned away in circumstances that resembled a trap," a statement issued by Paris lawyer firm Bourthoumieux said on behalf of the three lawyers, Jacques Verges, Lucie Bourthoumieux and Marcel Ceccaldi.
(Reporting by Stephanie Nebehay in Geneva, Mark John in Dakar, and Ange Aboa in Abidjan; writing by Richard Valdmanis)
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