UNITED NATIONS, May 15 (Reuters) - The U.N. Security Council on Friday voiced concern over reports that Eritrea has been supplying arms to Islamist militants intent on toppling Somalia's new government and condemned the recent violence.

The 15-nation council also demanded that Somali opposition groups immediately end the violence and join reconciliation efforts in the lawless Horn of Africa state.

"The Security Council ... expresses its concern over reports that Eritrea has supplied arms to those opposing the (government of) Somalia in breach of the U.N. arms embargo," the statement said.

It also called for an investigation of the reports.

In an accusation backed by some security experts and diplomats, Somalia's government said earlier this month that Asmara continues to support al Shabaab militants with planeloads of AK-47 assault rifles, rocket-propelled grenades and other weapons.

Eritrea rejects accusations that it sends weapons to the al Qaeda-linked Islamist militants fighting Somalia's government.

Fighting between al Shabaab militants -- who admit to having foreigners in their ranks -- and pro-government fighters has killed at least 139 people and sent some 27,000 fleeing the pock-marked, seaside capital Mogadishu since late last week.

Somalia's moderate Islamist leader Sheikh Sharif Ahmed was sworn in as the country's president in January, promising to forge peace with east African neighbors, tackle rampant piracy offshore and rein in hard-line insurgents.

Somalia has been a byword for anarchy since a dictatorship was overthrown in 1991. Currently, large parts of south and central Somalia are under the control of al Shabaab insurgents and allied Islamist fighters.

AlertNet news is provided by