A carefully choreographed assault on Kenya’s most upscale shopping mall was described by U.S. counterterrorism officials Monday as evidence that the militant group al-Shabab has turned its energies toward regional attacks after losing power and territory in its home base of Somalia.

Smoke continued to billow from the Westgate mall in Nairobi on Monday as Kenyan security forces pursued a team of al-Shabab gunmen who have killed at least 62 people and wounded dozens in a rampage that began Saturday.

U.S. officials said the assault showed levels of determination and sophistication that are likely to prompt American intelligence and military officials to reexamine the threat posed by al-Shabab, a militant group that aligned itself with al-Qaeda last year. Even so, U.S. officials said the attack reveals more about al-Shabab’s shifting survival strategies than any success it has had recapturing its former strength.

“They’re in much worse shape than they were a couple years ago,” said Rep. Adam B. Schiff (D-Calif.), a member of the House Intelligence Committee. “This may very well be an effort to send a message to the rest of the world that they’re still around, still violent. I think it also is an indication they fear for their survival if the [African Union] continues to press its campaign against them in Somalia.”

Kenya is among the A.U. nations that have contributed forces to a U.S.-backed campaign that since 2011 has forced al-Shabab to retreat from the Somali capital, Mogadishu, as well as other strongholds, including Kismaayo, a port city that had been a source of millions of dollars in annual tax revenue.

The losses have crippled al-
Shabab as an insurgency. But analysts at the CIA and other agencies say the group’s retreat from its effort to impose Islamist rule may have prompted its leaders to divert remaining resources to plotting attacks against countries that sent troops to Somalia.

“Al-Shabab’s operational arm may be benefiting from additional resources now that the group is less preoccupied with governance,” said an American official with access to classified U.S. intelligence on the Westgate attack. “It’s really too early to say if al-Shabab’s latest attack is the beginning of a broader campaign in Kenya or a desperate attempt to compel Nairobi to withdraw its troops from Somalia.”

U.S. officials and counterterrorism experts noted that the mall assault was preceded by dozens of smaller-scale strikes in Kenya over the past two years, including attacks with grenades and small arms that targeted churches, nightclubs and bus stations. Many were focused in towns along the Kenya-Somalia border, but the campaign has included strikes in Mombasa and Nairobi.

Al-Shabab has also attracted a small number of Kenyan fighters who support the group’s hard-line Islamist agenda. Among them was Ahmed Iman Ali, a former preacher who became a senior commander of al-Shabab in charge of the group’s non-Somali faction, according to an article published last year by the Combating Terrorism Center at the U.S. Military Academy at West Point.

Before the Nairobi assault, the most recent large-scale attack by al-Shabab was in 2010, when more than 70 people were killed in the bombings of crowds watching a televised soccer match in Uganda, which has backed the multinational campaign against al-Shabab.

The United States also has been deeply involved in that effort, providing military training to regional allies as well as intelligence gathered by the CIA and the National Security Agency. The U.S. military’s Joint Special Operations Command has carried out intermittent drone strikes and helicopter assaults against the group.

U.S. concern about al-Shabab intensified as the group became aligned with al-Qaeda, whose most potent affiliate is based in Yemen, across the Gulf of Aden from Somalia. U.S. officials suspect that several dozen Somali Americans left the United States to join al-Shabab in the past five years, raising fears that some might seek to return to carry out attacks.

Still, U.S. officials have recently characterized al-Shabab as primarily a regional menace.

In congressional testimony this year, Director of National Intelligence James R. Clapper Jr. said al-Shabab would probably “remain focused on local and regional challenges” and “continue to plot attacks designed to weaken regional adversaries, including targeting U.S. and Western interests in East Africa.”

Experts said that the Nairobi attack could help al-Shabab attract attention and financial support from sympathizers in Africa and the Middle East but that overall the group has been substantially degraded.

The attack may help “bring in donations from radicals elsewhere and draw some recruits,” said Daniel Benjamin, a professor at Dartmouth University who previously served as the top counterterrorism official at the State Department. But, he said, “the fact is al-Shabab, at least compared with its own aspirations, is a shadow of its former self.”

Julie Tate contributed to this report.