The Swiss Foreign Ministry says up to 34 Swiss are listed as missing following the September 11 terrorist attacks in New York and Washington.
"It is not possible to say exactly how many Swiss lost their lives in the attacks," said Walter Thurnherr of the foreign affairs ministry on Tuesday. "But we are confident that at least 10 more people will make themselves known."
Some of the families, friends and neighbours who wait to hear from their loved ones apparently provided the ministry with the wrong information on their missing relatives - fearing that they may have been in the United States when the attacks occurred.
Some of the missing were elsewhere on September 11, some of the relatives later learned.
A number of families have remained in close contact with the Swiss officials in the United States and at home. Some cantonal authorities offer them support under guidelines set out for victims of terrorist acts.
"We are in close contact with these people and are trying to offer them as much support as we can," Thurnherr told swissinfo.
Nearly 7,000 people are thought to have died in the attacks on the twin towers of New York's World Trade Center and on the Pentagon in Washington.
The Swiss authorities set up a hotline after the attacks to trace missing Swiss who were thought to be in the area. Only one Swiss person, who was aboard one of the planes used by the terrorists, has been confirmed dead.
swissinfo with agencies