(CBS/AP)-- 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.
The official spoke on condition of anonymity to disclose details about the private meeting.
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."
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. 16.
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."
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.
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. The U.S. says 1,429 people died, including 426 children.
The Britain-based Syrian Observatory for Human Rights, which collects information from a network of anti-regime activists, says it has so far only been able to confirm 502 dead.
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.
The report is expected later this month. Some European officials are asking the U.N. to speed up the investigation or issue an interim report.
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.
Kerry's trip overseas will last three days, meeting with European and Arab leaders in Lithuania, France and the United Kingdom.
Military planning is already under way to define the type of armed support provided by other countries in a proposed joint U.S.-France operation, a senior State Department official traveling with Kerry told CBS News correspondent Margaret Brennan.
While Kerry campaigns abroad, the Obama administration will try to court congressional votes to approve a limited military strike to degrade Assad's ability to launch another chemical attack.
For a president not known for investing heavily in consultations with Capitol Hill, the coming days represent one of the most intense periods of congressional outreach in President Obama's administration. Mr. Obama seeks to salvage a policy whose fate he's placed in lawmakers' hands, planning for himself and for aides a flurry of speeches, phone calls, briefings and personal visits to Democrats and Republicans alike.
The lobbying campaign culminates Tuesday, the evening before a key vote is expected in the Senate, when Obama will address the nation from the White House to make his case that America's military must once again raise arms to protect a value he says the world simply cannot afford to place in jeopardy.
In a series of hearings this week, three of the president's top national security advisers explained that unlike the U.S.-led invasion of Iraq, this narrowly defined action would not commit the U.S. to a war nor commits American troops. Instead, this "hit and run" action is meant to send a message to Assad and to degrade his ability to use chemical weapons. No outside power has taken action to halt neither the Assad regime's actions nor the increasingly brutal war that has killed more than 100,000 people since 2011.
The senior State Department official, who is very familiar with the Syrian opposition battling Assad on the ground, argued that a failure to act by the U.S. would further destabilize the region by driving up the flow of refugees. More than two million have fled into surrounding countries since the war began. Echoing Kerry's claims that the cost of inaction outweighs the risks, the official said a failure to act would likely boost support for al Qaeda-linked extremist groups, who are providing well-armed and trained fighters to battle Assad. Those extremists have begun to control territory and to target U.S.-backed moderate rebels in yet another front of the civil war.
The U.S. effort to cultivate a strong moderate rebel force has been limited in scope and success. While the Obama administration acknowledges that the strikes are not meant to end the "grinding war of attrition" that is likely to continue long after any strikes, the U.S. believes that the Assad regime is gradually losing control of Syria.
A senior official told reporters traveling with Kerry, that the State Department is beginning to help the moderate Syrian opposition establish "law and order" in areas that the Assad regime no longer controls. The U.S. will expand a program that provides training and communications equipment to a local police force in Aleppo. This is part of a campaign to help the moderate opposition gradually win support from the local communities.
On Mideast peace negotiations, Kerry urged his EU counterparts to consider delaying putting in place a funding ban on Israeli institutions operating in occupied territories.
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.
The Palestinians claim some of those territories — the West Bank, Gaza Strip and east Jerusalem — for their hoped-for state.
The EU ban applies to grants, prizes and financial instruments and that the new funding guidelines go into effect in 2014. The EU issues dozens of grants, totaling millions of euros, to Israeli universities, companies and researchers every year.