Updated 6:21 PM ET PARIS European foreign ministers on Saturday endorsed a "clear and strong response" to a chemical weapons attack that strongly points to the Syrian government, but they urged the U.S. to delay possible military action until U.N. inspectors report their findings. U.S. Secretary of State John Kerry, trying to make the Obama administration's case for a strike, thanked the European Union for a "strong statement about the need for accountability." Kerry said he would share his counterparts' concern with U.S. officials. A senior State Department official who attended Kerry's meeting with the ministers in Lithuania said Kerry made clear that the U.S. has not made any decision to wait. Later, at a news conference in Paris with French Foreign Minister Laurent Fabius, Kerry said "this is not the time to be silent spectators to slaughter" and that "this is not the time to allow a dictator unfettered use of some of the heinous weapons on earth." Fabius said that "punishment is not at odds with a political solution. ... Bashar Assad will not participate in any negotiation as long as he sees himself as invincible. White House lobbying Congress for support on Syria strike President Barack Obama has asked the U.S. Congress to approve the use of force. A final vote in the U.S. Senate is expected at the end of the coming week. A U.S. House vote is likely the week of Sept. CBS News chief White House correspondent Major Garrett reports that Mr. Obama will be continuing pressing his case, both the lawmakers and the public, next week, sitting down for interviews Monday with six major networks: CBS, NBC, ABC, Fox, CNN and PBS. A statement read at the end of the ministers' meeting by the EU's foreign policy chief, Catherine Ashton, said the Aug. 21 attack was a "blatant violation of international law, a war crime and a crime against humanity." Information from a wide variety of sources confirmed the chemical attack, according to the statement, and "seems to indicate strong evidence that the Syrian regime is responsible" as it is the only party "that possesses chemical weapons agents and the means of their delivery in a sufficient quantity." Syrian rebels prepare for U.S. strike The statement said a "clear and strong response is crucial to make clear that such crimes are unacceptable and that there can be no impunity." But at the same time, the statement said the EU backs the need to address the crisis through the U.N. process. The EU said it hoped a preliminary report of the investigation can be released as soon as possible and welcomed French President Francois Hollande's statement Friday to wait for this report before any further action is taken. Hollande indicated that a report could be issued by the end of next week. CBS News' Garrett reports Mr. Obama hopes the report will give him further momentum as he looks to clear the most significant congressional hurdle to military action: the House of Representatives, The U.S. blames the government of Syrian President Bashar Assad for the attack in the Damascus suburbs and, citing intelligence reports, says sarin gas was used. European officials have questioned whether any military action against the Assad government can be effective. Britain's Parliament has voted against military action. Hollande displayed sudden caution Friday, saying for the first time that he would wait for the U.N. report before deciding whether to intervene militarily. France, which firmly backs the Syrian rebels and has strategic and historic interest in the region, had been ready to act last week but held off when President Barack Obama declared last weekend that he would seek the backing of Congress first. Hollande's announcement appeared to catch Fabius off guard. Earlier Friday, Fabius told EU foreign ministers in Vilnius that there was no need to wait for the U.N. report because it would simply confirm what was already known - that the chemical weapons attack had occurred - but would not say who was responsible. While the diplomatic wheels turn, rebels in Syria are eaglerly awaiting action. CBS News correspondent Clarissa Ward, reporting from the Turkish side of the Syrian border, said rebel leaders she has spoken too have expressed concerned that further delays will allow Assad the opportunity to evade serious damage. Rebels are also worried about the nature of the strikes, should they happen. If they aren't strong enough to seriously erode the Assad regime's defenses, rebels and civilians could face severe retaliations. Syria militia says U.S. attack would be "start of World War III" Ashton said the EU would send a team to Israel on Monday to make sure the implementation of the ban is done "very sensitively." "We, of course, want to continue to have a strong relationship with Israel," she said. The EU's decision on the ban, announced in July, marked a new international show of displeasure with Israeli settlements built on lands captured in the 1967 Mideast war.