His comments stood in marked contrast to assurances of substantial progress in Somalia that other US officials have repeatedly voiced.
Al-Shabaab did lose territory last year and was weakened in its ability to generate resources, Gen Rodriguez said.
But he warned that Shabaab may respond to these financial and territorial losses “by broadening its terrorist agenda throughout East Africa.”
The group also retains the ability to stage lethal attacks inside Somalia, Gen Rodriguez acknowledged on the same day that other US military officials were reporting an air strike on a Shabaab compound that was said to have killed 150 militants.
Recent military operations against the Islamist insurgents “have been limited due to overstretched Amisom forces and endemic deficiencies within the Somali National Army.”
Shabaab may respond to its financial and territorial losses inside Somalia “by broadening its terrorist agenda throughout East Africa,” Gen Rodriguez warned.
He also noted that Shabaab is currently carrying out “almost daily lethal asymmetric attacks in Somalia against Amisom troops.”
The US commander’s appraisal suggested that intensive efforts by the US and other powers to improve the Somali state’s military and governance capabilities have produced few gains.
“The Somali National Army remains dependent on foreign forces to conduct operations and is challenged by leadership, logistical support and clan factionalism,” he told the US Senate panel.
“Under-governed areas outside the reach of the Federal Government of Somalia will continue providing Al-Shabaab with territory in which it can evade security forces and continue targeting East African regional governments and security interests as well as European and American interests,” the general added.
And there is little prospect that Somalia’s central government will function more effectively in the coming months, he said.
Political tensions within the government are likely to increase in the run-up to scheduled elections in August, Gen Rodriquez predicted.
These tensions “may be exacerbated,” he added, “if the government falls further behind on the key transitional benchmarks of constitutional reform, federal state creation, and the establishment of technical commissions to oversee the electoral process, or if it tries to exert its authority outside of a federally-styled government.”
Gen Rodriguez also sounded an alarm concerning “widespread deterioration of security situations” elsewhere in East Africa.
He attributed this negative trend to “contested elections and constitutional referendums.”
“As seen in Burundi,” the Africom chief said, “election protests can lead to politically motivated violence between the opposition, security forces, and civilian militias.”