The United States on Thursday offered Russia a broad new military partnership in Syria, hoping the attraction of a unified campaign against the Islamic State group and Al Qaeda — and a Russian commitment to ground Syria's bombers — could end five years of civil war. The deal, if finalized, could dramatically alter America's role in the conflict.

U.S. Secretary of State John Kerry was to present the new ideas to Russian President Vladimir Putin in the Kremlin on Thursday. The eight-page proposal, a copy of which The Washington Post published, shows the U.S. offering intelligence and targeting sharing, and even joint bombing operations — a pact Moscow long had wanted, but Washington resisted.

In Washington, White House spokesman Josh Earnest said Russia had to limit its targeting to extremist groups such as IS and the Nusra Front, Al Qaeda's Syrian affiliate, and not the more moderate opposition forces fighting Syrian President Bashar Assad's government.

"There's a clear contradiction in Russia's approach to this situation," he said. While Moscow often talks about terrorism, he said it uses its "military might to prop up the Assad regime at the expense, or in some cases even to the detriment, of our efforts to go after extremists."

The proposal would undercut months of U.S. criticism of Russia's military actions in Syria, such as those voiced by Earnest on Thursday, and put the United States alongside Assad's chief international backer, despite years of American demands for the Syrian leader to leave power.

Russia, which began intervening in Syria on Assad's behalf last September, would get what it wanted, leading an international anti-terrorism alliance.

Putin spokesman Dmitry Peskov recalled Putin's desire for a united, U.S.-Russian approach to battling the jihadi groups that have exploited the chaos in Syria and neighboring Iraq to emerge as global threats.

Much of Washington is wary about working too closely with Russia. A dissent cable signed by 51 State Department officials last month showed a sizable part of America's diplomatic establishment believing a U.S. military response against Assad's forces was necessary.

Opposition to this latest Syria plan is shared by a significant number of officials at the State Department and Pentagon and among U.S. intelligence agencies, according to several American officials.

The Obama administration has few other options right now.

Suggestions of U.S. force don't carry much weight, given the unfulfilled threats throughout the war. There were declarations five years ago that Assad's days were "numbered," and President Barack Obama vowed a military response if chemical weapons were used, then backed down in 2013.

The proposed, U.S.-Russian "Joint Implementation Group" would be based near Amman, Jordan. At its most basic level, the former Cold War foes would share intelligence and targeting information. They "should coordinate procedures to permit integrated operations," if the U.S. and Russia decide such operations are in their interests, the leaked document said.

The proposal would address one of the most persistent problems with enforcing a cease-fire in Syria: the Nusra Front. The group is engaged in a variety of local alliances with other rebel groups the U.S. and its Arab allies want shielded by the cessation of hostilities. Nusra's fighters are often embedded with such groups on the battlefield or move between various fighting formations.

For that reason, the U.S. has almost entirely avoided bombing Nusra targets in recent months. Russia hasn't hesitated. As Russia has taken out Nusra forces, the U.S. says Russia also has killed hundreds of moderate, anti-Assad fighters and civilians, undermining chances for peaceful diplomacy.

The new offer represents a new recognition by the U.S. that Nusra must be defeated to end the fighting. Its offensives southwest of Aleppo have been viewed as particularly damaging to the truce.

The document puts responsibility on Russia to get Syria's air force out of the sky, with some limited exceptions. It would subject Russian strikes against vetted Nusra targets to American approval.

Moscow's biggest responsibility would be one it has been reluctant to assume: getting Assad to start a political transition that ends his family's four-decade hold over the country. Russia supports the vague idea of "transition," but has never publicly spoken of Assad having to resign.

Reactions among U.S.-backed rebel groups in Syria were mixed.

Capt. Abdelsalam Abdurrazek, a spokesman for Nur al-Din Zenki, a CIA-screened rebel entity fighting near Aleppo, decried the U.S. for offering "to support an ally of the Syrian regime and an enemy of the Syrian people." He said his group would continue fighting alongside Nusra.

Mozahem al-Saloum of the New Syrian Army, which is fighting IS in eastern Syria, blamed Nusra for paving the way for IS, and said the U.S. plan could work if it guarantees Assad's departure. Al-Saloum, the group's spokesman, demanded "an immediate transitional period."

Two months ago, Kerry said the transition had to start on Aug. 1, or Syria and its backers are "asking for a very different track." Any Plan B has remained undefined beyond vague hints of a military intervention involving Saudi troops. The White House and Pentagon have resisted a greater U.S. role.