The Obama administration worked Monday to preserve thinning hopes for a political deal that could end the Syrian civil war and to hold off rising pressure from lawmakers and Syria’s Arab neighbors for more direct U.S. involvement.

An assassination bid against Syria’s prime minister in the capital, Damascus, suggested that rebels are increasingly bringing the two-year-old conflict to the doorstep of President Bashar al-Assad. Both sides are engaged in a military standoff in much of the country, and Damascus is presumed to be the prize that would signal military victory.

Syrian Prime Minister Wael al-Halki had a narrow escape when a car bomb exploded near his convoy Monday morning as it moved through an upper-class Damascus neighborhood. State television said Halki was unharmed, but at least nine people were killed and 17 injured.

Syrian government officials said the attack showed that the rebels are not interested in negotiations.

In Washington, Secretary of State John F. Kerry sought to persuade Lakhdar Brahimi, the U.N.-Arab League envoy to Syria, to remain on the job. Brahimi has been on the verge of quitting for weeks, given the failure of his efforts inside and outside Syria to foster a diplomatic resolution. His departure would erode the Obama administration’s main diplomatic argument that a political settlement can be reached.

Interactive Grid: Keeping track of the conflict in Syria through videos, images and tweets.

On Monday, Arab foreign ministers also met with Kerry in a session led by Qatar. Qatar is one of two Persian Gulf nations known to be arming the Syrian opposition, and several other nations have quietly concluded that Islamist extremists are among the recipients. Vice President Biden briefly joined the meeting, according to participants.

More forceful U.S. role urged

Several of Syria’s Arab neighbors, led by close U.S. ally Jordan, are lobbying for a more forceful U.S. role in Syria. There is no consensus about what the United States should do, however. Options include giving heavier gear to the rebels, providing protection for refugees or rebel fighters with missile batteries or aircraft, or authorizing precision airstrikes to destroy chemical weapons stockpiles or key air defenses.

The U.S. announcement last week that Syrian government forces are likely to have used sarin, a nerve agent, has fueled bipartisan congressional demands for better protection of Syrian refugees or more help to the rebels. Lawmakers who have been most critical of the administration’s stance, including Sen. John McCain (R-Ariz.), said the apparent use of chemical weapons crosses the threshold that President Obama had set for U.S. intervention.

Obama, however, has insisted on additional proof to buttress the U.S. intelligence assessments. Intelligence agencies concluded with moderate to high confidence that Syria has used the internationally banned weapons, but they cited potential problems with the evidence, said officials familiar with the findings. They spoke on the condition of anonymity to discuss the assessments.

The White House has said only that the findings were reached with “varying degrees of confidence.”

“There is much more to be done to verify conclusively that the red line that the president has talked about has been crossed,” White House press secretary Jay Carney said Monday.

U.N. Secretary General Ban Ki-moon, meanwhile, renewed an appeal for Syria to allow U.N. chemical weapons experts into the country, saying that on-site inspections are essential to “establish the facts and clear up all the doubts” about any use of chemical weapons.

Ban’s remarks — delivered with chief U.N. chemical weapons inspector, Ake Sellstrom, at his side — followed allegations by several countries, including Britain and France, that the Syrian government probably used chemical arms in recent months.

The main agenda for Kerry’s meeting with the Arab League was to follow up on his efforts to jump-start Israeli-Palestinian peace talks. He wants to use a dormant Arab League peace proposal as one template.

Tough task for U.N. envoy

Before Kerry’s private meeting with Brahimi, State Department spokesman Patrick Ventrell said, “The purpose is to encourage him [Brahimi] to continue in his good work.”

The veteran Algerian diplomat has gotten almost nowhere in his mission to rally the United States and Russia, Assad’s chief international backer, around a transition plan for Syria. Washington and Moscow blame each other for the impasse. Brahimi told U.N. diplomats last week that his efforts to bring Syrians together have fared even worse.

“I haven’t resigned,” the envoy told reporters at the United Nations this month. “Every time I wake up and I think I should resign, but I haven’t.”

Brahimi’s efforts were complicated by the Arab League’s recent endorsement of the Syrian political opposition, leaving him with less leverage with Assad and with Russia. He wants to stop the international flow of weapons to both sides to persuade Assad and the rebels to the bargaining table. He has said that the conflict cannot be won militarily, a view that many in the Obama administration share.

The White House said Obama discussed Syria with Russian President Vladimir Putin during a phone call Monday, with Obama “underscoring concern over Syrian chemical weapons.”

“The presidents agreed to stay in close consultation” and instructed Kerry and Russian Foreign Minister Sergei Lavrov to continue discussions on the issue, the White House said. The two diplomats met last week, shortly after Kerry announced a modest expansion of U.S. support for the Syrian rebels, but appeared no closer to bridging their disagreement.

A Russian statement on the conversation did not mention chemical weapons but said that Kerry and Lavrov were “in constant contact and . . . trying to develop some joint steps.” Putin aide Yuri Ushakov said the two presidents stressed “the readiness to take all necessary measures to finally resolve the Syrian issue,” Russia’s Interfax news agency reported.

Russia holds a veto at the U.N. Security Council and has blocked stronger action there to punish Assad or support the rebels.

Hauslohner reported from Beirut. Ahmed Ramadan in Beirut, Colum Lynch at the United Nations and Karen DeYoung in Washington contributed to this report.