A series of bombings in Mogadishu shows that the Islamist al-Shabaab movement, allied to al-Qaida, remains a lethal force despite the loss of key Somali strongholds to a U.N.-backed African force last fall.

The attacks, and threats of more bombings directed at senior government officials, could jeopardize efforts by President Hassan Sheik Mohamud to persuade the United States, Britain and nearly 50 other donor nations meeting in London to produce a "Marshall Plan for Somalia."

There's a lot riding on the London conference. The United States and the European Union have spent billions of dollars in recent years to put Somalia, battered by incessant civil war since 1991, back on its feet in the face of a stubborn al-Shabaab insurgency.

On Sunday, a car bomb intended to assassinate high-level government officials in Mogadishu killed seven people, four of them passersby, at the K4 roundabout, the busiest junction in the war-scarred Indian Ocean city.

Caught in the attack were six aid officials from the gas-rich Persian Gulf emirate of Qatar traveling in a convoy of Interior Ministry cars.

Officials say the apparent target was the minister, Abdikarin Hussein Guled, who heads the government campaign to crush al-Shabaab but he wasn't in the motorcade.

There were two car bombings in the north of the city the same day, although no casualties were reported.

But al-Shabaab's military spokesman, Sheik Abdiasis Abu Musab, warned that more attacks were on the way to hammer Somalia's new government installed after elections in late 2012.

On April 14, a string of attacks in Mogadishu killed 19 people in one of the most deadly and coordinated assault in months. Al-Shabaab claimed responsibility.

In one of three attacks, gunmen wearing Somali army uniforms -- three of them with suicide vests -- stormed the city's main courthouse, killing lawyers, court officials and bystanders. Security personnel battled the attackers, with several people killed the fierce crossfire.

In another attack that day, gunmen attacked Turkish aid workers at Mogadishu airport. Al-Shabaab branded them "Western mercenaries" in an attack that appeared to be intended as a warning to foreign aid groups to stay away from Somalia.

The attacks demonstrated how al-Shabaab is able to infiltrate the heavily guarded capital with apparent ease, which observers say is demoralizing government and security officials who fear being targeted.

Until 2011, al-Shabaab controlled most of Mogadishu, with the government penned up in a small enclave around the presidential palace and parliament.

But in August 2011, a U.N.-mandated "peacekeeping force" from the African Union, composed mainly of troops from Uganda and Burundi, pushed the Islamists out of the capital.

Later, the force, known as Amisom, was expanded and aided by military interventions by Kenyan and Ethiopian forces from the south and west, aided with "foreign" airstrikes and U.S., French and British intelligence, began pushing al-Shabaab out of its main strongholds outside Mogadishu.

Last September, Kismayu, a port south of Mogadishu and al-Shabaab's key urban base, was taken. The Islamists turned to guerrilla warfare, and, despite internal rifts largely between nationalist groups and foreign al-Qaida jihadists, began a new terrorist campaign of bombings and assassinations.

The group still operates in the southern countryside and its main objective now is to dislodge Mohamud's government, elected after al-Shabaab's defeat and described by the Financial Times as the "most promising and representative in years."

It was recognized by the United States in January, ending a hiatus of 20 years, and by the International Monetary Fund in April.

The Americans are determined to support Mohamud, the first Somali leader in years untainted by corruption or the clan feuding that has ravaged Somalia since the overthrow of dictator Mohammed Said Barre by warlords in 1991.

But peace and a political settlement in a land riven by clan rivalries still seem far off at present, largely because of al-Shabaab's new insurgency.

Mohamud, a 57-year-old academic, told the London conference, which began Tuesday, that security is his first priority right now.

On Sept. 12, 2012, he narrowly escaped assassination as he met foreign dignitaries in Mogadishu's Jazeera Hotel soon after his surprise election.

Two suicide bombers and two gunmen dressed in army uniforms attacked the gathering. Ten people were killed, but Mohamud, and the visiting dignitaries, survived.