UNITED NATIONS — The U.N. Security Council warned Thursday that "internal and external pressures risk undermining Somalia's political unity" and expressed serious concern at the ongoing threats posed by the al-Shabab Islamic extremist group.

A presidential statement approved by the 15-member council calls for stepped-up efforts "to prevent destabilizing effects of regional crises and disputes from spilling over into Somalia" and to support the country's federal system and institutions.

Somalia, which borders restive Kenya and lies across the Gulf of Aden from conflict-wracked Yemen, began to fall apart in 1991, when warlords ousted dictator Siad Barre and then turned on each other. Years of conflict and attacks by al-Shabab, along with famine, shattered the country of some 12 million people. It has been trying to rebuild since establishing its first functioning transitional government in 2012.

Al-Shabab, which is fighting to impose Shariah law across Somalia, was pushed out of the capital, Mogadishu, and other major urban cities more than two years ago. But the extremist group still carries out suicide attacks across Somalia.

The presidential statement coincided with meetings in Somalia's capital, Mogadishu, on Thursday between U.N. political chief Rosemary DiCarlo and senior government officials, U.N. spokesman Stephane Dujarric said.

He said she reiterated U.N. support for the country and quoted DiCarlo as saying that "the unity of Somalis is essential to advance federalism, reduce violence, defeat extremism and tackle the humanitarian challenges and deliver real benefits to the population."

With a new federal government established, pressure is growing on Somalia's military to assume full responsibility for the country's security. But there are serious concerns about the military's takeover as a 21,000-strong African Union force known as AMISOM begins a withdrawal that is expected to be complete in 2020. and 2021.

The Security Council expressed "deep concern" at the humanitarian situation in Somalia, including the risk of famine and impact of recent flooding, and urged continued international support.