HANOI, Vietnam — Thousands of Vietnamese living illegally in America now face deportation after the two countries completed an agreement yesterday, a move that sparked worry among immigrant communities.

Vietnamese who entered America illegally after the former foes normalizedrelationsin1995could now be forced to return to their birth country, the director of U.S. Immigration and Customs Enforcement, Julie Myers, said.

The deal has been under negotiation for 10 years. Vietnam had previously been reluctant to accept citizens back, and community leaders in America said many immigrants have been living with deportation orders for years, even decades.

“Some Vietnamese have been here have a very long time,” an organizer with VietUnity, an Oakland-based Vietnamese community organization, Carolyn Tran, said. “They don’t have a connection there any more.”

More than 1.5 million overseas Vietnamese — the largest population outside Vietnam — live in America. Many fled their native country in boats after the Vietnam War ended in 1975 and northern communist forces took control of the former South Vietnam, which the U.S. had backed.

Critics of the agreement wonder whether this pact won’t be rolled back to include others who entered the United States in the 70s and 80s.

“There is concern,” said Joren Lyons, a staff attorney with the Asian Law Caucus in San Francisco, which has represented dozens of Vietnamese facing deportation orders. “Vietnam has said for decades no, these people can’t be returned to Vietnam, and now they’re saying yes. So is this a foot in the door? Will they start accepting people who came earlier as well?”