Renewed diplomatic efforts to halt Libya's civil war appeared to be gaining momentum Thursday as NATO airstrikes once again hammered Moammar Gadhafi's stronghold of Tripoli.

Officials in the capital say they are open to international efforts that would bring an end to four months of fighting between forces loyal to the longtime leader and rebels who control the eastern third of the country along with pockets in the west.

But they insist that Gadhafi will not bow to international pressure to push him aside.

"We don't accept anything that may be done against him. He is a red line in our discussions," Prime Minister al-Baghdadi al-Mahmoudi said. Any deal that would partition the country is also unacceptable, he added.

One of Gadhafi's sons told an Italian newspaper that while his father would not seek exile, elections under international supervision could offer a way out. A vote could be organized within three months, he said.

The son, Seif al-Islam, told Corriere della Sera that Gadhafi would step aside if he lost, which the son said was unlikely. He acknowledged, however, that "my father's regime as it developed since 1969 is dead."

In Washington, U.S. State Department spokeswoman Victoria Nuland rejected the idea of elections in Libya.

"It's a little late for any proposals by Gadhafi and his circles for democratic change," she said Thursday. "It's time for him to go."

Gadhafi's son, once groomed to succeed the elder Gadhafi, has served as one of his main spokesmen during the conflict. Like Gadhafi himself, he has been heard from rarely in recent weeks.

Russia's envoy to Libya met with senior government leaders in Tripoli — but apparently not Gadhafi himself — hours after NATO warplanes pounded the area near the leader's Bab al-Aziziya compound.

Russian envoy Mikhail Margelov met in Tripoli with al-Mahmoudi and Foreign Minister Abdul-Ati al-Obeidi.

The Interfax agency quoted Margelov as saying, after meeting the foreign minister, that he was told "Gadhafi is not prepared to leave, and the Libyan leadership will talk about the country's future only after a cease-fire."

The foreign minister also said, according to Margelov, that the African Union should be "the main force" in reaching a resolution.

Spain ordered the expulsion of the Libyan ambassador in Madrid, saying Gadhafi's regime no longer has legitimacy. A Foreign Ministry statement Thursday said the government gave Ajeli Abdussalam Ali Breni 10 days to leave the country. Three other diplomatic staffers were also ordered out.

The latest NATO strike near Gadhafi's compound rattled windows across the heart of the capital, producing thunderous concussions and smoke billowing into the air.

Canadian warplanes involved in bombing

The Canadian military confirmed on Thursday that Canadian warplanes took part in bombing the Libyan capital of Tripoli.

CF-18 jet fighters took part in four days of targeted strikes over last weekend, said Col. Alain Pelletier, who commands Canada's air contingent in Italy.

The Canadian jets were involved in day and night raids on Tripoli.

NATO launched its air campaign nearly three months ago under a United Nations resolution to protect civilians. What started as a peaceful uprising inside the country against Gadhafi and his more than four-decade rule has become a civil war.

Fighting between government forces and the rebels had reached a stalemate until last week when NATO launched the heaviest bombardment of Gadhafi forces since the alliance took control of the skies over Libya.

Speaker rejects Obama's Libya claim

Meanwhile, the leader of the U.S. House of Representatives on Thursday rejected President Barack Obama's contention that U.S. forces face no hostilities in Libya, saying the argument doesn't "pass the straight face test."

Responding to increasing anger in Congress over its refusal to seek its authorization for the military intervention, the administration sent to Congress a report saying that because the U.S. is in a supporting role in the NATO-led bombing mission, American forces are not facing the "hostilities" that would require the president to seek such approval under the War Powers Resolution.

The 1973 law prohibits the military from being involved in actions for more than 60 days without congressional authorization, plus a 30-day extension. The Libya campaign has gone on for nearly three months and leader Moammar Gadhafi has maintained his grip on power.

Republican House Speaker John Boehner joined several Republicans and Democrats in expressing incredulity over the White House's "no hostilities" claim.

"Yet we've got drone attacks under way. We're spending $10 million a day, part of an effort to drop bombs on Gadhafi's compound," Boehner told reporters at a news conference. "It doesn't pass the straight face test in my view that we're not in the midst of hostilities."

Boehner threatened to cut off funds for the operation, with possible House action next week.

"The Congress has the power of the purse, and certainly that is an option," Boehner said.

In a letter to Obama this week. Boehner said the commander in chief will clearly be in violation of the War Powers Resolution on Sunday and he pressed the administration to state the legal grounds for Obama's actions. The Republican said Thursday the White House report failed to answer his questions and he expects a response by his Friday deadline.