The Syrian opposition figure tasked with forming an interim government to administer rebel-held areas has resigned, citing an inability to do so.
In a statement, Ghassan Hitto said he would "continue working for the interests of the revolution".
His decision follows a leadership overhaul by the National Coalition.
Ahmed Jarba was named leader of the main opposition alliance on Saturday as Saudi-backed candidates defeated those allied with Qatar in several elections.
On Monday, Mr Jarba warned that there was a "real humanitarian disaster" in the central city of Homs and said he was prepared to offer President Bashar al-Assad a truce during the Islamic holy month of Ramadan to stop the fighting there.
As government forces continued an offensive on opposition-held districts of Homs, state media said the army had killed "terrorists" in several areas, including Bab Houd in the Old City and several outlying towns.
The Syrian Observatory for Human Rights reported that Bab Houd and al-Safsafa had been hit by heavy artillery and tank fire on Monday.
The UK-based activist group said troops had also captured about a fifth of the besieged northern district of Khalidiya. A government official had earlier claimed that the entire district was under army control.
A car bomb also exploded in the predominantly Alawite and Christian area of Akrama, killing at least four people, officials and activists said.
Baath leadership change
The violence in Homs and elsewhere in Syria has left civilians in rebel-held areas in dire need of humanitarian assistance, opposition and humanitarian activists say.
In March, Mr Hitto was tasked by the National Coalition for Syrian Revolutionary and Opposition Forces with forming an interim government to administer so-called "liberated" zones, co-ordinating the provision basic services and supplies.
However, Mr Hitto was mistrusted by many members of the opposition alliance, who saw him as too close to the Muslim Brotherhood and Qatar, and he has been effectively side-lined since.
The National Coalition's former president, Moaz al-Khatib, believed the creation of an interim government was premature and announced his resignation five days after Mr Hitto's appointment.
On Monday, Mr Hitto said he was standing down as prime minister after being unable to form an administration.
"I emphasise I will continue working for the interests of the revolution and towards achieving its objectives," he added.
Mr Jarba, an influential tribal figure with close links to Saudi Arabia, meanwhile said he expected advanced weapons supplied by Saudi Arabia to reach rebel fighters "soon" and that they would change the military balance in Syria.
He also said the National Coalition would not attend peace talks in Geneva planned by the US and Russia unless its military position improved.
"If we are going to go to Geneva, we have to be strong on the ground, unlike the situation now, which is weak," he told the Reuters news agency.
In a separate development on Monday, Syria's ruling Baath Party announced that it had elected a new regional command, replacing its ageing leadership, including Vice-President Farouq al-Sharaa.
State TV said the 16 members of the top decision-making body were chosen during a meeting of the party's central committee.
"The Baath Party must develop to strengthen a culture of dialogue... and deepen interaction with citizens to overcome the negative effect of the crisis," President Assad was quoted as saying.
Among the new members of the regional command are parliamentary speaker Jihad al-Laham and Prime Minister Wael al-Halqi.
During nearly five decades in power in Syria, the Baath Party has evolved from an Arab nationalist movement into a vast organisation that has infiltrated every aspect of public life.
Although a large number of low-ranking officials have publicly left the party since the start of the uprising in March 2011, its main leadership bodies have remained steadfastly loyal to Mr Assad.