Libya’s prime minister called for a cease-fire Thursday, saying for the first time that the government would be willing to talk to the rebels, but the White House immediately rejected the offer as not credible.

The Libyan government has called for a cease-fire several times since a NATO bombing campaign began in mid-March, but it has in the past refused to acknowledge the Transitional National Council — the rebels’ de facto government — as a legitimate negotiating partner.

It was unclear Thursday just how much ground Prime Minister Baghdadi al-Mahmoudi had given. “The time has come for serious negotiations,” he said. “We have not conceded to anything,” he said shortly thereafter.

Mahmoudi said Libya was asking the United Nations and the African Union to work out the timing of a cease-fire, and he invited international observers to verify that it was taking place.

But he stopped short of saying that all military personnel would be put back in their barracks, something the European Union has said would be a necessary part of any negotiations.

In mid-March, the Libyan government announced that it had unilaterally ceased military operations after the U.N. Security Council took action against it, but residents at the time said that the government had actually escalated its attacks.

U.S. deputy national security adviser Ben Rhodes said Thursday that such offers must be backed up by action. Rhodes said that Moammar Gaddafi’s government is not complying with a U.N. resolution intended to protect the Libyan people, the Associated Press reported.

South African President Jacob Zuma is scheduled to visit Tripoli on Monday with other African leaders to help negotiate an end to the three-month-old conflict.

Part of the problem appears to be Gaddafi’s future role. Western leaders have said he needs to step down, but differences appear to be emerging about the precise timing of that move.

At a news conference in London on Wednesday, British Prime Minister David Cameron said Gaddafi should step down and leave the country, calling for “turning up the heat.”

President Obama, speaking at the same event, appeared to leave the door open to Gaddafi remaining in power during a transitional period, saying the campaign to get him to step down would be a “slow, steady process.”

Mahmoudi said that only Gaddafi would determine his future role. “It is he who decides what the Libyan people want,” he said.

Western officials say the international effort to pressure Gaddafi appears to be having an impact.

“We understand that Gaddafi was spending nights in hospitals and rarely ever staying two nights in the same place,” said a senior British government official who is working on Libya issues. Gaddafi, he added, “is avoiding pre-arranged meetings.”

“He’s obviously acting in a paranoid manner, moving around, moving his family around, to places he thinks are safe, he thinks he can’t be targeted at,” the official said.

Mahmoudi refused to answer questions about Gaddafi’s ability to communicate with the government, saying only that he was “in good health and he fulfills his duty normally.”

NATO pounded Tripoli with airstrikes earlier this week, perhaps explaining the latest cease-fire request.

The coalition said it used 28 bunker-busting bombs near the Gaddafi compound Tuesday morning, striking what it said was a vehicle storage facility. A government spokesman said the attack was simply a failed attempt to assassinate Gaddafi.

The Libyan government has not allowed reporters to see the results, but one journalist who made an unauthorized trip into Tripoli on Thursday saw damage in a compound next to Gaddafi’s sprawling residential center.

A roughly 15-foot-high concrete wall was heavily damaged in at least six places, and it had been patched in areas with corrugated metal. In one spot where the wall had not been repaired, large hangar-like structures could be seen in pieces inside. The Libyan government said three people were killed and 150 were injured.

At least four additional airstrikes hit the area around Gaddafi’s compound Thursday night.