BEIRUT, Lebanon -- Iraq's branch of Al Qaeda said Tuesday that it had merged with the Nusra Front, a group of jihadists fighting to topple President Bashar al-Assad of Syria, in a marriage that appeared to strengthen the role of Islamic militants in the Syrian insurgency and further complicate Western assistance efforts.
The United States has already blacklisted the Nusra Front over evidence of its links with the Islamic State of Iraq, the Qaeda branch. But the news of the merger, made by the branch's leader, Abu Bakr al-Baghdadi, in an audio statement posted on jihadist Web sites, was the first time he had announced that they were a single organization.
"The time has come for us to announce to the people of the Levant and to the whole world that Al Nusra Front is merely an extension of the Islamic State of Iraq and a part of it," Mr. Baghdadi said. He also said the combined group would be called the Islamic State in Iraq and the Levant and would dedicate half its budget to the Syrian insurgency.
In a warning to other Syrian fighters who want Mr. Assad to go but do not share Mr. Baghdadi's views, he said, "Don't make democracy a price for those thousands among you who have been killed."
Mr. Baghdadi's announcement came as a backlash appeared to be spreading in Syria over the indiscriminate civilian killings believed to be carried out by jihadist groups, including the Nusra Front, aimed at further weakening Mr. Assad's power in the two-year-old conflict. These groups have fearsome fighters but do not take orders from the Free Syrian Army, the rebels' main fighting organization, which has criticized attacks on civilians and sought to distance itself from a recent spree of car bombings, including a horrific blast in central Damascus on Monday that left at least 15 people dead.
The jihadist merger also comes as Secretary of State John Kerry hinted during a trip to the Middle East and Europe that the United States was preparing to step up its assistance to the Syrian rebel cause.
While the United States and other Western nations have backed the Free Syrian Army and contributed nonlethal aid to its combatants, American officials have been reluctant to supply weapons, particularly because of concerns that they could fall into the hands of the Nusra Front or affiliates loyal to Al Qaeda. Differences in the degree of Western commitment to the insurgency have been a source of frustration to the Syrian political opposition.
The opposition movement also has struggled with its own divisions over rebel behavior. On Tuesday, the Syrian Observatory for Human Rights, an anti-Assad group based in Britain, accused a rogue insurgent battalion operating in Aleppo of arresting, torturing and extorting dozens of residents, mostly between the ages of 18 and 20.
"The Syrian Observatory demands that this battalion stop engaging in these practices immediately, as such behavior does not represent the values of the revolution," said the group, whose information network inside Syria has emerged as a major source of insurgency news. "On the contrary, they are an extension of the oppressive and brutal methods practiced by the Syrian security apparatus."
In Geneva, the United Nations refugee agency said Tuesday that the pace at which families are fleeing the destruction in Syria threatens to double or even triple the number of total refugees seeking shelter in neighboring countries by the end of the year. The agency also renewed an urgent appeal for money to deal with the crisis.
"The numbers look horrendous," Panos Moumtzis, the refugee agency's regional coordinator for Syrian refugees, told reporters.
A year ago, the number of Syrian refugees stood at 30,000, and the figure now exceeds 1.3 million, he said. With 200,000 people fleeing across Syria's borders every month and no political solution in sight, humanitarian agencies fear that they will be trying to support up to three million refugees by the end of the year, Mr. Moumtzis said.
Hania Mourtada reported from Beirut, and Rick Gladstone from New York. Nick Cumming-Bruce contributed reporting from Geneva.
This article originally appeared in The New York Times.