Syrian rebels battling the regime of President Bashar al-Assad have begun receiving significantly more and better weapons in recent weeks, an effort paid for by Persian Gulf nations and coordinated in part by the United States, according to opposition activists and U.S. and foreign officials.

Obama administration officials emphasized that the United States is neither supplying nor funding the lethal material, which includes antitank weaponry. Instead, they said, the administration has expanded contacts with opposition military forces to provide the gulf nations with assessments of rebel credibility and command-and-control infrastructure.

“We are increasing our nonlethal assistance to the Syrian opposition, and we continue to coordinate our efforts with friends and allies in the region and beyond in order to have the biggest impact on what we are collectively doing,” said a senior State Department official, one of several U.S. and foreign government officials who discussed the evolving effort on the condition of anonymity.

The U.S. contacts with the rebel military and the information-sharing with gulf nations mark a shift in Obama administration policy as hopes dim for a political solution to the Syrian crisis. Many officials now consider an expanding military confrontation to be inevitable.

Material is being stockpiled in Damascus, in Idlib near the Turkish border and in Zabadani on the Lebanese border. Opposition activists who two months ago said the rebels were running out of ammunition said this week that the flow of weapons — most still bought on the black market in neighboring countries or from elements of the Syrian military — has significantly increased after a decision by Saudi Arabia, Qatar and other gulf states to provide millions of dollars in funding each month.

Syria’s Muslim Brotherhood also said it has opened its own supply channel to the rebels, using resources from wealthy private individuals and money from gulf states, including Saudi Arabia and Qatar, said Mulham al-Drobi, a member of the Brotherhood’s executive committee.

The new supplies reversed months of setbacks for the rebels that forced them to withdraw from their stronghold in the Baba Amr neighborhood of Homs and many other areas in Idlib and elsewhere.

“Large shipments have got through,” another opposition figure said. “Some areas are loaded with weapons.”

The effect of the new arms appeared evident in Monday’s clash between opposition and government forces over control of the rebel-held city of Rastan, near Homs. The Britain-based Syrian Observatory for Human Rights said rebel forces who overran a government base had killed 23 Syrian soldiers.

Administration officials also held talks in Washington this week with a delegation of Kurds from sparsely populated eastern Syria, where little violence has occurred. The talks included discussion of what one U.S. official said remained the “theoretical” possibility of opening a second front against Assad’s forces that would compel him to move resources from the west.

Syria will also be on the agenda at this weekend’s NATO summit in Chicago, according to administration officials.

Although the alliance has repeatedly said it will not become involved in Syria, Turkey has indicated that it may invoke Article IV of the NATO Charter, which would open the door to consultations on threats to Turkish security and consideration of mutual defense provisions of Article V of the charter.

Last month, after Syrian forces fatally shot four fleeing Syrians who had crossed into Turkey, Turkish Prime Minister Recep Tayyip Erdogan said that under Article V, “NATO has responsibilities to protect the Turkish border.”

The Turks, who have grown increasingly anxious about the growing conflict in their neighboring country, have resisted direct military involvement without the international legitimacy of a United Nations Security Council resolution. Efforts to pass a resolution authorizing any intervention beyond humanitarian aid have been blocked by opposition from Russia and China.

But Turkey’s position has been evolving, with military officials who once opposed any kind of non-political intervention now seeing the region becoming increasingly involved in the crisis. Shiites and Sunnis in neighboring Lebanon battled this week over the Syrian situation, raising concern both in Ankara and Washington.

Officials in the region said that Turkey’s main concern is where the United States stands, and whether it and others will support armed protection for a safe zone along the border or back other options that have been discussed.

The United States and its allies remain formally committed to a U.N. peace plan being spearheaded by former secretary general Kofi Annan. Nearly two-thirds of an authorized 300 unarmed U.N. military monitors have arrived in Syria, with the rest due by the end of this month.

But even Annan has acknowledged the initiative has failed so far to significantly quell the violence or make progress toward a political transition. U.S. officials have said they feel constrained from declaring the mission a failure, at least until the full complement of monitors arrives. Annan himself has expressed pessimism over prospects for success.

Opposition figures said they have been in direct contact with State Department officials to designate worthy rebel recipients of arms and pinpoint locations for stockpiles, but U.S. officials said that there currently are no military or intelligence personnel on the ground in Syria.

The Pentagon has prepared options for Syria extending all the way to air assaults to destroy the nation’s air defenses. U.S. officials, however, have said that such involvement remains very unlikely. Instead, they said, the United States and others are moving forward toward increased coordination of intelligence and arming for the rebel forces.

The Sunni-led gulf states, which would see the fall of Assad as a blow against Shiite Iran, would welcome such assistance, but they would like a more formal approach. One gulf official described the Obama administration’s gradual evolution from an initial refusal to consider any action outside the political realm to a current position falling “between ‘here’s what we need to do’ and ‘we’re doing it.’”

“Various people are hoping that the U.S. will step up its efforts to undermine or confront the Syrian regime,” the gulf official said. “We want them to get rid” of Assad.

Since the uprising began early last year, U.S. efforts to promote a political solution have been stymied by Assad’s political intransigence and his ongoing military assault on Syrian towns and cities, as well as the opposition’s failure to agree on a unified political leadership or game plan.

Despite administration hopes that the Sunni-led Syrian National Congress would become an umbrella organization, it has failed to win support from minority Syrian Christians, Kurds, Druze and Assad’s Alawite sect. All have resisted what they say is the group’s domination by the Muslim Brotherhood.

The Free Syrian Army, the opposition military force, has resisted direction from the fractured political opposition. Its troops, many of them Syrian army defectors, are said to operate in independent entities spread across Syria, leading the United States and others in the past to express caution about assisting them.

Sly reported from Beirut.