BEIRUT — Syrian President Bashar Assad came under a new barrage of international pressure Tuesday, with the Turkish foreign minister urging him to stop killing protesters and U.S. officials saying the Obama administration is preparing to explicitly demand his departure.

Even as Assad held more than six hours of talks with the visiting Turkish minister, his military unleashed fresh attacks on restive areas, attacks that activists said killed more than 20 people.

Turkish Foreign Minister Ahmet Davutoglu said he met the Syrian leader for more than six hours in the capital Damascus and discussed “concrete steps” to end the violent crackdown on protesters. Rights groups say about 1,700 people have been killed since March. An aggressive new military offensive that began with the Muslim holy month of Ramadan a week ago has killed several hundred.

On his return to Turkey, Davutoglu said the talks were cordial but did not say what specific steps they had discussed or whether Assad had agreed to consider them.

“We discussed ways to prevent confrontation between the army and the people and tensions like those in Hama in the most open and clear way,” Davutoglu said, referring to the Syrian city that has become a flashpoint in the five-month-old uprising against Assad’s autocratic rule.

“The coming days will be important to see if the expectations are being met. We hope that internal peace and calm is achieved and steps for reform are taken.”

The Syrian regime has shown no signs of scaling back its crackdown despite increasing diplomatic isolation.

In Washington, officials said the administration will call outright for Assad to give up power and hit the regime with tough new sanctions. The State Department signaled for the first time that American efforts to engage the Syrian government are finally over. The White House is expected to lay out the tougher line by the end of this week, possibly Thursday.

The officials said the move will be a direct response to Assad’s decision to step up the ruthlessness of the crackdown against pro-reform demonstrators by sending tanks into opposition hotbeds. The officials spoke on condition of anonymity to discuss internal administration deliberations.

President Obama and other top U.S. officials previously had said Assad has “lost legitimacy” as a leader and that he either had to spearhead a transition to democracy or get out of the way. They had not specifically demanded that he step down. The new formulation will make it clear that Assad should leave power.

Other countries are also stepping up the pressure. Envoys from India, Brazil and South Africa were expected to meet with Syrian officials in Damascus today, part of a broad diplomatic push to stop the killings.