The Friends of Yemen group of donor nations plans to meet in May in Riyadh to encourage political transition in the troubled Arabian Peninsula state against a backdrop of mounting violence, Britain said on Friday.

The meeting, which will include Gulf and European states and the United States, is the group's third and comes amid an escalation of violence by a resurgent al Qaeda, which has exploited months of political turmoil to expand in Yemen.

Current Yemeni President Abd-Rabbu Mansour Hadi took office last month under a plan crafted by the Gulf Cooperation Council (GCC) with U.S. backing, after a year of massive protests against his predecessor Ali Abdullah Saleh.

The recent deterioration of political cooperation in Yemen is concerning and we call upon all groups to engage constructively in transition, Britain's Foreign Office said in a statement, announcing that the next Friends of Yemen meeting would be held in the Saudi capital on May 23.

Britain, Saudi Arabia and Yemen co-chair the group.

The statement included an official message from the body, which lauded Hadi's inauguration on February 25, and said the international community now had to support government reforms.

Tackling economic and security challenges in Yemen is of paramount importance, as is creating an inclusive political environment through national dialogue, said the group, which also called for the rejection of violence.

Under the GCC power transfer plan, Hadi was elected for a two-year transitional period to restructure the armed forces and oversee the drafting of a new constitution.

Critics say Saleh's relatives remain in control of the security establishment and armed forces, fanning suspicions that Hadi is incapable of standing up his predecessor's allies.

(Reporting by Mohammed Abbas; Editing by Mark Heinrich)