WASHINGTON - In a show of Western solidarity, President Obama and French President Francois Hollande vowed Tuesday to escalate airstrikes against the Islamic State and bolster intelligence sharing following the deadly attacks in Paris. They called on Russia to join the international efforts, but only if Moscow ends its support for Syria's embattled president.

"Russia is the outlier," Obama said during a joint White House news conference with Hollande.

Tuesday's meeting came hours after Turkey shot down a Russian warplane near the Syrian border. The incident underscored the complex military landscape in Syria, where a sprawling cast of countries and rebel groups are engaged on the battlefield and in the skies overhead, sometimes with minimal coordination.

Obama said Russian cooperation in the fight against the Islamic State would be "enormously helpful." But he insisted a partnership is impossible as long as Russia stands by Syrian President Bashar al-Assad, who is blamed by the United States for plunging his country into chaos and creating the vacuum that allowed the Islamic State to strengthen.

"We hope that they refocus their attention on what is the most substantial threat, and that they serve as a constructive partner," Obama said of Russia.

Hollande concurred, saying that France wants to work alongside Russia, but only if President Vladimir Putin "fully commits" to supporting a political transition in Syria.

Hollande's alignment with Obama was notable, given that he was expected to urge the U.S. president to put aside some of his differences with Russia to build a new coalition to fight the extremists. But Hollande's mission quickly became entangled with the fallout from the downed Russian military plane.

Even before the incident between Turkey and Russia, Hollande faced a tough challenge in getting Obama to agree to a partnership with Moscow. The White House is deeply skeptical of Putin's motivations, given his longstanding support for Assad, and has accused Putin of bombing rebels fighting the Syrian leader instead of targeting the Islamic State.

Hollande will meet with Putin Thursday in Russia, part of his diplomatic effort to build support for an intensified campaign against IS.

The terror group is blamed for the Nov. 13 attacks in Paris that killed 130 people and wounded hundreds more at restaurants, a concert venue and outside a soccer stadium.

The attacks in the heart of Europe sparked fears of terrorism in the U.S., as well as an outpouring of solidarity with the French.

Obama spoke warmly of America's affection for France, noting that he keeps a photograph by his bed of his wife, Michelle, and him kissing in the city's Luxembourg Gardens.

Hollande welcomed the U.S. show of unity, but suggested he was more interested in concrete actions than kind words.

"The Paris attacks generated a lot of emotions," he said through an interpreter. "But that's not enough. We must act."

Obama and Hollande pledged to increase airstrikes against extremist targets, take back Islamic State-controlled territory in Iraq and Syria, and focus more on disrupting the terrorists' financial networks.

However, Hollande joined Obama in refusing to intervene militarily on the ground in Iraq and Syria, saying that is a role for local forces.

Shortly after their meeting, a French official in Washington said French warplanes had struck an Islamic State command center located west of the Iraqi city of Mosul.