U.N. experts who collected samples from last week's alleged chemical weapons strike outside Damascus left Syria for the Netherlands on Saturday, hours after President Barack Obama said he is weighing "limited and narrow" action against the Syrian regime his administration blames for the attack. In Moscow, Russian President Vladimir Putin urged Obama not to rush into a decision. The Russian leader implied the chemical attack came from among the rebels, saying he was convinced it was a provocation carried out by those who wanted to draw in the United States. If the Americans have evidence to the contrary they should present it to the United Nations inspectors and the U.N. Security Council, he said. Russia is one of Syrian President Bashar Assad's staunchest allies. Putin's comments were his first on the crisis since the suspected chemical weapons attack on rebel-held suburbs of Damascus on Aug. 21. In Syria, rebels fighting to topple Assad said they plan to go on the offensive against his troops in attacks timed to coincide with the U.S. strikes. "Zero hour begins the moment the first missile is fired," said Qassem Saadeddine, a senior rebel commander and spokesman for the rebels' Supreme Military Council. "As the (U.S.) strikes gets under way, we will launch attacks against military airports, command centers, missile bases and military checkpoints," the former army colonel told The Associated Press from his base in Turkey. Several other rebel commanders based in the rebel-held suburbs of the capital, Damascus, confirmed they would exploit the U.S. action to try and advance on the capital, seat of Assad's power. Still, some opposition fighters said they felt uneasy about the prospect of U.S. strikes on their country, calling the U.S. objectives vague and "suspicious." The U.N. inspectors spent three days this week touring stricken areas near Damascus and a fourth day interviewing patients at a government-run military hospital. They wrapped up their investigation Friday and left Syria on Saturday, via Lebanon. The team then flew to the Dutch city of Rotterdam aboard a German government-chartered plane, the German Foreign Ministry said. The experts had taken blood and urine samples from victims as well as soil samples from the affected areas for examination in laboratories in Europe. The U.N. has said it will try to expedite its final report. U.N. disarmament chief Angela Kane is to brief Secretary-General Ban Ki-moon later Saturday on the investigation. With the inspectors out of Syria, the looming confrontation between the U.S. and Assad's regime moves one step closer to coming to a head. The Obama administration has made clear that it is confident in its assessment and could act before the U.N. releases the results of its probe.