BEIRUT — Turkey’s prime minister on Tuesday called for the first time for Bashar al-Assad to step down, in a fiery speech that likened the Syrian leader to Hitler and Mussolini and marked the final crumbling of Turkish-Syrian relations, according to analysts.

“Without spilling any more blood, without causing any more injustice, for the sake of peace for the people, the country and the region, finally step down,” Recep Tayyip Erdogan said, urging Assad to look to the fate of Libyan leader Moammar Gadhafi, who was toppled by an internationally backed uprising and, last month, was killed.

The admonition, delivered in an address to Erdogan’s ruling AK party, came after several days of increasingly stern Turkish warnings to Assad to end an ongoing military crackdown on nationwide protests against his government. It also followed an attack on Turkish pilgrims in neighboring Syria on Monday, allegedly by Syrian security forces.

“This is a relationship which is now permanently broken, which is remarkable given the speed at which it has happened,” said Salman Shaikh of the Brookings Institution. Syria and Turkey have for the past decade been building a strong trade and diplomatic relationship, with personal bonds between their leaders.

“What Erdogan says is significant, because he is the most popular leader in the Arab world, despite not being Arab,” Shaikh added. Popular opinion among Arab leaders has recently turned against Syria; the Arab League has designated a ministerial council to discuss the crisis, and it is set to meet Thursday to debate measures including sanctions against Assad’s government.

The escalation of political pressure is motivated by the apparent conviction among the Turkish leadership that Assad is unlikely to recover from the cycle of protest and violence in Syria and that his days as leader are numbered, said Henri Barkey, a professor of international relations at Lehigh University in Pennsylvania. Turkey seeks to use its influence to ensure that Assad’s 11-year rule ends as quickly as possible, to avert civil war and economic collapse in its neighbor, he said.

The hardening of Turkey’s stance could open the door to stronger measures, including sanctions, arming Syrian opposition groups or creating a militarized buffer zone within Syria, manned by Turkish troops, according to observers.

However, there are obstacles to these measures. Many Turkish businesses, especially in the south of the country, engage in extensive trade with Syria and would object to sanctions. Arming the Syrian opposition or intervening with Turkey’s military could risk triggering civil war or border conflict.

Turkey is more likely to look to the Arab League to take the next steps, or to the United Nations, where on Tuesday the General Assembly’s human rights committee passed a resolution drafted by Britain, France and Germany that condemns “grave and systematic human rights violations by the Syrian authorities.” The resolution was immediately dismissed by Syria’s U.N. ambassador, Bashar Ja’afari, who called the motion part of an American campaign against his country.