Cairo (CNN) -- Three American college students suspected of throwing Molotov cocktails in Cairo's Tahrir Square will be detained another four days as an investigation continues, said a spokesman for the office of Egypt's general prosecutor.
"A bag filled with empty bottles, a bottle of gasoline, a towel and a camera was found with them," spokesman Adel Saeed said late Wednesday.
"They denied the bag belonged to them and said it belonged to two of their friends," Saeed added.
The mother of at least one of the students detained said Wednesday that she was able to speak to him briefly in a telephone call arranged by U.S. diplomats.
"He sounded scared, but he said he was OK," Joy Sweeney said of her son, Derrik Sweeney, one of the three American college students being held for questioning.
A U.S. State Department official told her husband the three may have a hearing Thursday, she said.
Derrik Sweeney said he and his friends had done nothing wrong, Joy Sweeney told CNN's Erin Burnett on Wednesday night.
"He is a very bright kid with a good heart who believes in all the people in the world," said Joy Sweeney. "And he really wanted to learn more about the Egyptian culture."
The students first met with an American diplomat Wednesday morning, according to a spokeswoman for American University in Cairo.
"He reports that they are in good health and being treated well," Morgan Roth said of the U.S. consul general's visit with the students, who have been in custody since Monday.
Before their visit with the consul, the students were questioned again by Egyptian authorities, this time with a U.S. Embassy lawyer present.
Wednesday marked the fifth day of violent clashes between security forces and protesters demanding that the country's military leaders step aside. Similar protests forced President Hosni Mubarak to relinquish power in February.
Sweeney, Gregory Porter and Luke Gates are university students from different schools attending American University in Cairo on a semester-long, study-abroad program, according to the school.
Sweeney, 19, is a Georgetown University student from Jefferson City, Missouri; Porter, 19, from Glenside, Pennsylvania, attends Drexel University in Philadelphia; and Gates, 21, of Bloomington, Indiana, goes to Indiana University.
Social-media posts appear to show Gates and Sweeney in the thick of recent protests in Cairo, with Gates indicating he had been injured in clashes over the weekend.
"Earlier tonight rubber bullets a charge and then a retreat," said a message posted Sunday from a Twitter account with Gates' name and a photo resembling one of the men in a police video. The poster added that his knee and elbow were hurt.
On Saturday, the writer said that "we were throwing rocks and one guy accidentally threw his phone."
Another Facebook account shows a man resembling Sweeney during protests in Cairo.
CNN could not independently confirm the authenticity of the posts.
Gates' father and Sweeney's mother said in interviews that their children have had a long interest in other cultures.
Joy Sweeney, speaking Wednesday on CNN, said she doesn't believe her son is guilty of violence.
"He's very peaceful, harmonious," she said. "He cares about the world. He cares about people and I can't imagine him ever doing something to hurt someone."
CNN's Mohamed Fadel Fahmy and Kara Devlin contributed to this report.