French President Francois Hollande expressed readiness Friday to push ahead with plans to strike Syria for allegedly using chemical weapons, despite the British parliament’s rejection of military action, and Germany’s declaration that it would not participate. Washington was understood to be preparing for the possibility of a strike against the Damascus regime within days.

“The chemical massacre of Damascus cannot and must not remain unpunished,” Hollande said in an interview with the newspaper Le Monde, published Friday, as UN experts in Damascus began what is expected to be the last day of their probe into the alleged attack.

The French president reiterated that France wants a “proportional and firm action.” When asked about the type of intervention, however, he said “all options are on the table.”

Hollande suggested that action could even come ahead of Wednesday’s extraordinary session of the French Parliament, called to discuss the Syria situation; lawmakers’ approval is not needed for Hollande to order military action.

“I will not take a decision before having all the elements that would justify it,” he told Le Monde. However, noting that he had convened parliament, he added: “And if I have (already) committed France, the government will inform (lawmakers) of the means and objectives.”

The British parliament voted late Thursday against military action in Syria, whittling down the core of the planned coalition to the United States and France. Italy and Germany have said they won’t take part in any military action. Guido Westerwelle, the German foreign minister, was quoted Friday as saying his country had not been asked to particpate in any strike, and “neither are we contemplating it.”

Hollande’s remarks came a day after the French news site Le Point reported on Thursday that France had dispatched the advanced frigate Chevalier Paul from the Mediterranean port of Toulon to the eastern Mediterranean.

The British ‘no’ vote raised questions about France’s participation — and ratcheted up pressure on US President Barack Obama. Facing skepticism at home, the US administration shared intelligence with lawmakers aimed at convincing them the Syrian government used chemical weapons against its people and must be punished.

Despite roadblocks in forming an international coalition, Obama appeared undeterred and advisers said he would be willing to retaliate against Syria on his own.

“The president of the United States is elected with the duty to protect the national security interests in the United States of America,” White House spokesman Josh Earnest said.

Even before the vote in London, the US was preparing to act without formal authorization from the United Nations, where Russia has blocked efforts to seek a resolution authorizing the use of force, or from Capitol Hill. But the US had expected Britain, a major ally, to join in the effort.

France has more intimate ties to Syria, having once ruled the country; it also has warplanes and strategic interests in the region. Paris has embraced the Syrian opposition and urged a firm response against Assad over the purported August 21 chemical weapons attack outside Damascus. But Hollande appears to be facing increasing political and public resistance against moving against Syria quickly.

Hollande said that France is among the few nations capable of “inflicting a sanction by the appropriate means” and “it is ready.” But a decision will be made in close coordination with allies, he added.

French military analysts say France’s most likely role would be from the air, including use of Scalp cruise missiles that have a range of about 500 kilometers (300 miles), fired from Mirage and Rafale fighter jets. French fighters could likely fly directly from mainland France — much as they did at the start of a military campaign against Islamic radicals in Mali earlier this year — with support from refueling aircraft. France also has six Rafale jets at Al Dhafra air base, near Abu Dhabi in the United Arab Emirates on the Persian Gulf, and 7 Mirage-2000 jets at an air base in Djibouti, on the Red Sea.

Hollande reiterated that any action is aimed at punishing the regime of Bashar Assad, not toppling him.

“I won’t talk of war but of a sanction for a monstrous violation of the human person. It will have a dissuasive value,” he said.

Russian Foreign Minister Sergey Lavrov has warned that military strikes would lead to long-term destabilization of Syria and the region. He has spoken against any use of force without UN Security Council approval, which he said would be a “crude violation of international law.” Russia has a veto at the Security Council, and has remained a strong ally of Syria throughout the civil war, which has left more than 100,000 people dead.

In Damascus, three UN vehicles headed out for more on-site visits on Friday, after an early morning delay.

The UN said Thursday that the inspectors would wrap up their investigation Friday and leave Syria for the Hague, Netherlands, the following day. Some of the experts will travel to laboratories in Europe to deliver the material they’ve collected this week during trips to the Damascus suburbs purportedly hit by toxic gas.

Russian President Vladimir Putin’s foreign policy adviser expressed puzzlement Friday at why the UN team was leaving so soon.

“We don’t quite understand why the entire team had to be going back to the Hague when there are many questions about a possible use of chemical weapons in other areas in Syria,” said Yuri Ushakov.

The mandate of the UN team is to determine whether chemical agents were used in the attack — not who was responsible. But the UN has suggested that evidence collected by investigators — including biological samples and interviews — might give an indication of who was behind the attack.

Hollande said that a chemical attack is “an established fact … and the question is to know who are the authors of this frightening act.” But he reiterated what France has said for several days, that Paris has a “range of indices which point to the responsibility of the regime.”