PARIS—France and Britain stepped up calls Monday for other world powers to isolate Libya’s Moammar Gadhafi with a no-fly zone, amid diplomatic differences over how much backing to give Libyan rebels.  The accelerated push came as U.S. Secretary of State Hillary Clinton and other top diplomats from the Group of Eight prominent world economies met in Paris for a previously planned foreign ministers meeting.

France, which has angered some allies by offering diplomatic recognition to Libya’s opposition, said it is important to act urgently against “barbarity” by Gadhafi’s forces.

French President Nicolas Sarkozy and British Prime Minister David Cameron, in an letter to the EU president last week, said they supported “continued planning to be ready for all possible contingencies” in the Libyan situation—”including a no-fly zone or other options against air attacks.”

On Monday, Cameron said that time was of essence in responding to the situation in Libya, and NATO was drawing up contingency plans for a no-fly zone.

“Every day Gadhafi is brutalizing his own people. Time is of the essence,” Cameron told the parliament in London. “There should be no let up in the pressure we put on this regime.”

He added: “No one is talking about invasion or boots on the ground.”

Insurgents who control much of eastern Libya have called for a no-fly zone, as forces loyal to Gadhafi strike back with tanks and planes—pressing eastward against the rebels Monday.

British Foreign Secretary William Hague said Libyans will face a “nightmare” if Gadhafi regains control, insisting that the world is “reaching a point of decision” on whether foreign forces will impose a no-fly zone.  Hague also said he “wouldn’t exclude” amending a ban on arms exports to Libya so that weapons could be shipped to the rebels—but that talks with allies on that are needed.

The Arab League has backed a no-fly zone, and Hague told BBC Radio Monday that “in cases of great, overwhelming humanitarian need” one could be enforced without a U.N. Security Council resolution.  French Foreign Ministry spokesman Bernard Valero, speaking to The Associated Press, pointed to an “urgency” to act because violence against civilians was increasing in Libya. He said France also was working on a list of sanctions against Gadhafi’s regime at the U.N. Security Council.

Other countries, including the United States, have been more cautious.  Germany’s foreign minister, Guido Westerwelle, acknowledged that the Arab League supported a U.N.-approved no-fly zone, “but at the same time, it rejected any form of foreign, international intervention.”  “These are questions that have to be discussed, these are not clear signals being sent, because a no-fly zone would be a military intervention,” he said in Berlin.

Westerwelle said the Arab League would need to “not just support but also participate” in any action beyond targeted sanctions. He also stressed that Germany and other European countries don’t want to be drawn into a long-lasting war in North Africa.

Italy, a G-8 member that has close economic ties to Libya, has said it would support a no-fly zone, but is against unilateral actions by its allies. Before flying to Paris, Foreign Minister Franco Frattini said Italy believes the Libyan crisis requires “an immediate cease-fire accompanied by international measures.”  He echoed the sense of urgency.  “If these decisions come too late, they nullify the goal of preventing Gadhafi from carrying out a massacre,” Frattini said. A no-fly zone could be a deterrent, he said.

Turkish Prime Minister Recep Tayyip Erdogan, however, said that a foreign military intervention would not work.

“We have unfortunately seen from previous examples that external interventions, especially through military means, do not contribute to solutions, on the contrary, they deepen them,” Erdogan said. “Therefore, we regard a NATO intervention on Libya or any other country to be extremely useless, and furthermore, we fear that it would yield dangerous results.”