By Louis Charbonneau

UNITED NATIONS (Reuters) - A confidential U.N. monitors' report warns of "systematic abuses" by Somalia's government, which the monitors say has allowed the diversion of weapons Somali authorities purchased after the U.N. Security Council eased an arms embargo on Mogadishu last year.

Some of the arms believed to have been diverted in the conflict-torn Horn of Africa nation were earmarked for a leader of the al Qaeda-linked Islamist militant group al Shabaab, the monitors said in their report, which was obtained by Reuters.

In their 14-page report to the Security Council's sanctions committee, the U.N. Somalia and Eritrea Monitoring Group recommends either restoring the full arms embargo or at least tightening notification and reporting requirements related to arms deliveries.

"The Monitoring Group has identified a number of issues and concerns over current management of weapons and ammunition stockpiles by the Federal Government of Somalia (FGS), which point to high-level and systematic abuses in weapons and ammunition management and distribution," the report said.

The monitoring group is a panel of independent experts that track compliance with the U.N. Somalia-Eritrea sanctions regime.

The council's decision to ease Somalia's decades-old arms embargo last March was a controversial one. Some members of the 15-nation council disagreed with it, although Washington supported the Somali government's appeals for relaxing restrictions to enable it to better arm its security forces to fight al Shabaab.

The new report details difficulties the monitors have had in getting access to weapons stockpiles in Somalia and information about the country's growing arsenal. It says the government canceled several inspections of Somali armories the monitors and U.N. officials in Somalia had planned to undertake.

The monitors describe how parts of shipments of weapons from Uganda and Djibouti, including assault rifles, rocket launchers, grenades and ammunition "could not be accounted for." The report also mentioned discrepancies about what had happened to arms sent from Ethiopia.

"Given the gaps in information ... it is impossible to quantify what the scale of diversion of weapons stocks have been," the report said. "However, the Monitoring Group has obtained other pieces of qualitative evidence that point towards systematic abuses by the (Somali army)."

AL SHABAAB

The Security Council imposed the embargo on Somalia in 1992 to cut the flow of weapons to feuding warlords, who a year earlier had ousted dictator Mohamed Siad Barre and plunged the country into civil war. Somalia held its first vote since 1991 in 2012 to elect a president and prime minister.

For two decades Somalia was virtually lawless.

The monitors' report said that it has identified at least two clan-based "centers of gravity" for arms procurement within Somali government structures that are distributing arms to "parallel security forces and clan militias that are not part of the Somali security forces."

One of those groups is within the Abgaal sub-clan of Somali President Hassan Sheikh Mohamud, who last month said he wanted the U.N. Security Council to extend the partial lifting of the embargo beyond its March expiry because government troops needed more and better equipment to battle al Shabaab.

The monitors' report said "a key adviser to the president, from his Abgaal sub-clan, has been involved in planning weapons deliveries to al Shabaab leader Sheikh Yusuf Isse ... who is also Abgaal."

The report also referred to the role played by a Somali government minister from the sub-clan Habar Gedir in relation to arms purchases from a "foreign government in the Gulf" - a government the report does not identify.

"The Monitoring Group has received credible evidence of un-notified weapons deliveries by air from the Gulf state to Mogadishu during the course of October 2013, which would constitute a direct violation of the arms embargo," it said.

"Indeed, after delivery, some of the weapons were moved to a private location in Mogadishu," the monitors said.

The easing of the U.N. arms embargo has allowed sales of such weapons as automatic assault rifles and rocket-propelled grenades, but left in place a ban on surface-to-air missiles, large-caliber guns, howitzers, cannons and mortars as well as anti-tank guided weapons, mines and night vision weapon sights.

"The trends described above demonstrate that the implementation of the (government's) security policy is being captured by clan and sub-clan politics," the report said.

"Weapons distribution along clan lines for the prosecution of clan warfare is ultimately reducing the prospect of a cohesive strategy by the (government) against al Shabaab."

The report said private arms markets have popped up in Mogadishu where weapons diverted from the army have been sold.

The monitoring group presented eight options for the arms embargo next month when the current easing of weapons-import restrictions expires. The options it offers the Security Council range from lifting the arms embargo altogether to restoring the full embargo and possibly adding new measures.

The monitoring group recommends either restoring the full embargo as it was before the restrictions were eased last year or at least keeping it as is and introducing stricter rules regarding notifying and reporting to the U.N. sanctions committee regarding arms sales to Somalia.

It also suggests the possibility of beefing up the U.N. mission in Somalia by attaching a verification team to it that would track arms deliveries and stockpiles in Somalia.

(Editing by Ken Wills)