A Pakistani court on Monday accepted a government request to seek life sentences for five Americans already jailed for 10 years on terror convictions.
The five young men were found guilty in the eastern city of Sargodha last June of waging war against the state and funding a terrorist group.
They have appealed, but no date has been set for a new hearing. Prosecutors are now demanding that the court toughen their sentences to life imprisonment.
Deputy public prosecutor Rana Bahktiar told AFP that he lodged the request with a two-judge panel on behalf of the Punjab provincial government.
"The court will now hear our petition simultaneously with the appeal filed by the five boys against their conviction," Mr Bakhtiar said.
Prosecutors believe the men planned to travel to neighbouring Afghanistan and join Taliban-led militants fighting US and Nato troops.
Investigators claim the Sargodha five planned to travel to South Waziristan, a training ground for Islamist militants in Pakistan's lawless tribal belt that was targeted by a major military operation in 2009.
The defendants — Umar Farooq, Waqar Hussain, Rami Zamzam, Ahmad Abdullah Mini and Amman Hassan Yammer — pleaded not guilty, saying they came to attend a wedding and wanted to go on to Afghanistan to do humanitarian work.