With security forces and the army tightening the blockade of their hideout, the kidnappers of five Italian tourists moved their hostages on Tuesday, officials said.
The government has threatened to use force to free the three women and two men, despite pleas from the Italian government for continued negotiations.
The tribal officials, who refused to give their names fearing retribution, said the hostages still were in the rugged and mountainous Sirwah region of Marib province, about 120km northeast of San'a. They were kidnapped in the area on Sunday.
The tribal officials said that the kidnappers were persisting in their demand that fellow tribesmen be freed from Yemeni prisons in return for release of the hostages.
With the central negotiating process at a dead end, Sheik Darham al-Damaa, secretary-general of the Jahem local council in Marib Province and one of the key negotiators, said other tribal officials might be asked to join the talks.
Yemeni officials, however, did not appear ready for continued negotiations.
"The government will deal with an iron fist with those elements. This is terrorism, and we hit back against terrorist actions, we will hit back against kidnapping," Yemeni Prime Minister Abdul-Kader Bajammal said.
Yemen's official news agency SABA quoted an unnamed senior Interior Ministry official as saying "there would be no leniency with those criminals who tarnished the nation's reputation, harmed its economic interests."
"The situation is very complicated, and the army is about to launch an attack against the kidnappers," another Interior Ministry official told reporters on Tuesday, on condition of anonymity, because he was not authorized to talk with reporters.
About 4,000 Yemenis, meanwhile, protested in the Yemeni capital San'a against the recent rash of kidnappings.