Benghazi, Libya (CNN) -- An explosion rocked Benghazi's main square on Tuesday, prompting witnesses to say it was the work of the country's longtime strongman, Moammar Gadhafi.
A rebel spokesman used a speaker phone to address a crowd that gathered after the incident, calling the explosion a terrorist act by Gaddafi fighters who allegedly infiltrated Libya's rebel-held eastern city.
CNN could not independently confirm that statement.
Witnesses said two cars were damaged in the square, but there were no immediate reports of casualties.
Small arms fire could be heard immediately after the explosion, but that quickly subsided.
The incident occurred two days after government forces pounded rebel-held areas in Tripoli, in the wake of Libyan authorities reporting that a NATO air-strike killed one of Gadhafi's sons and three of his grandchildren.
Also Tuesday, a crowd described by one U.S. official as an "organized mob" marched on the U.S. Embassy in Tripoli, and crowds also gathered outside the British, French, Italian and Qatari embassies, officials said.
Pro-Gadhafi forces stepped up their shelling of rebel positions in Misrata after Libya's government reported the deaths in Gadhafi's family.
Tuesday's incidents came as Turkish Prime Minister Recep Tayyip Erdogan called on Gadhafi to step down.
"A new period (has) started in the history of Libya," Erdogan told reporters in Istanbul.
"At this point what needs to be done is for Moammar Gadhafi, who is holding the government in Tripoli in Libya, to leave power immediately and to fulfill his historical and humanitarian responsibility," Erdogan said.
Meanwhile, at the United Nations in New York, the French ambassador to the United Nations told journalists that there are no preconditions for Libyan cease-fire talks to occur and that Gadhafi need not step down for a cease-fire to be discussed.
French Ambassador Gerard Araud briefed reporters Tuesday as he assumed this month's presidency of the Security Council. He told reporters that "all of us are looking for a political solution" to the conflict in Libya and that there are "no preconditions" to a negotiation.
Libya has been embroiled in war between pro-Gadhafi and opposition forces, with NATO using air power to enforce a U.N. Security Council resolution to protect civilians threatened by Gadhafi troops.
CNN's Joe Vaccarello at the United Nations contributed to this report.