With focus still on the collapse of Bashar Assad’s government, there are signs fighting is dramatically escalating in northeast Syria. The area is held by U.S.-backed Kurds, while Turkey-supported rebel groups have gone on the offensive there, aided by Turkish airpower.

The Turkish rebels have attacked the territory controlled by the Kurds, who helped the U.S. defeat the Islamic State in eastern Syria. There are fears that Turkey -- which has waged a long war against the Kurds and considers the U.S.-backed group to be a terrorist group -- will use the chaos in Syria to now force them back.

There are reports the Turkish-backed rebels are now advancing on Kobani, an important Kurdish-majority town on Turkey’s border. It comes a day after the rebels successfully drove the Kurds from the key town of Manbij in northern Syria.

There are concerns that if Turkey and its rebel proxies press on against the Kurds it could endanger the containment efforts against the Islamic State. The Kurds currently guard 50,000 Islamic State prisoners in camps and are also essential to prevent the group regaining a foothold.

There are calls from some for the U.S. to warn Turkey to pull the rebels back.

-ABC News' Patrick Reevell

Secretary of State Antony Blinken reaffirmed the U.S.'s "full support for a Syrian-led and Syrian-owned political transition."

"This transition process should lead to credible, inclusive, and non-sectarian governance that meets international standards of transparency and accountability," Blinken said in a statement Tuesday.

"The Syrian people will decide the future of Syria. All nations should pledge to support an inclusive and transparent process and refrain from external interference. The United States will recognize and fully support a future Syria government that results from this process. We stand prepared to lend all appropriate support to all of Syria’s diverse communities and constituencies," Blinken said in a statement.

Blinken added that it must also "fully respect the rights of minorities, facilitate the flow of humanitarian assistance to all in need, prevent Syria from being used as a base for terrorism or posing a threat to its neighbors, and ensure that any chemical or biological weapons stockpiles are secured and safely destroyed."

-ABC News' Shannon K. Kingston

The Hayat Tahrir al-Sham rebels have begun to form a new government as they seize power in Damascus, Syria. The group has appointed Mohammed al-Bashir as the new prime minister, according to state media outlet SANA.

Al-Bashir has previously held leadership roles and he will run the new government until March.

Israel destroyed the Syrian navy's fleet overnight in a "large-scale operation," according to the Israel Ministry of Defense.

"The IDF has been operating in Syria in recent days To harm and destroy strategic capabilities that threaten the State of Israel. The Navy operated last night to destroy the Syrian fleet with great success," Israel Defense Minister Israel Katz said in a statement Tuesday.

"I hereby warn the rebel leaders in Syria: Whoever follows Assad's path will end up like Assad - we will not allow an extremist Islamic terrorist entity to act against Israel across its border and at the risk of its citizens, we will do everything necessary to remove the threat," Katz said.