MOGADISHU, Somalia — An elderly Italian nun who devoted her life to helping the sick in Africa was shot dead by two gunmen at a hospital yesterday in an attack possibly linked to worldwide Islamic anger toward Pope Benedict XVI.

Sister Leonella, 65, was shot in the back four times by pistol-wielding attackers as she left the Austrian-run S.O.S. hospital at lunchtime after finishing nursing school for trainee medics. Her bodyguard was also slain.

No one claimed responsibility for the attack, which came just hours after a leading Somali cleric condemned the pope’s remarks last week on Islam and violence.

The head of security for the Islamic militia that controls much of southern Somalia, Yusuf Mohamed Siad, said one man had been arrested and that the second was being hunted. He said the killing might have stemmed from the uproar over the pope but stressed that he did not know for sure.

“They could be people annoyed by the pope’s speech, which angered all Muslims in the world, or they could have been having something to do with S.O.S.,” he said. “We will have to clarify this through our investigation.”

The Vatican called the killing a “horrible episode,” and President Napolitano of Italy denounced it as a “horrendous crime.”

“A woman who had dedicated her life to the service of the weakest, the most defenseless, and the neediest, beyond any ethnic or religious distinction, has been hit,” Mr. Napolitano said.

Sister Leonella, whose birth name was Rosa Sgorbati, had lived and worked in Kenya and Somalia for 38 years, her family said.

A doctor at the hospital, who would give his name only as Dr. Teckle, said she helped to teach and to look after children. “She was a dedicated and organized teacher,” he said. Her body was flown to Nairobi, Kenya, before being returned to Italy, he said.

Like many foreigners, Sister Leonella traveled with a bodyguard in this Horn of Africa nation, which slid into chaos after warlords overthrew Somalia’s longtime dictator in 1991. A Swedish journalist, Martin Adler, was shot dead in June during a demonstration in Mogadishu.

An Islamic militia seized control of Mogadishu in recent months and has extended its control over much of southern Somalia, challenging a weak, U.N.-backed interim government that has not been able to exert any power outside its base in Baidoa, 150 miles from the capital.

The militia has imposed strict religious rule in the areas under its sway, and its Islamic courts are credited with bringing a semblance of order, but many in the West fear a Taliban-style regime could emerge.

Several witnesses to yesterday’s shooting speculated that it was tied to the furor over Benedict’s discussion last week, which included quoting a 14th-century text that called some of Prophet Muhammad’s teachings “evil and inhuman.”

“I am sure the killers were angered by the pope’s speech in which he attacked our prophet,” Ashe Ahmed Ali, who was among those who saw the nun shot down at the hospital’s entrance, said. Earlier in the day, a leading Islamic cleric in Somalia had condemned the pope for offending Muslims.

“The pope’s statement at this time was not only wrong but irresponsible as well,” the deputy leader of the Somali Muslim Scholars Association, Sheik Nor Barud, said.