UN leader Ban Ki-moon says more than 100,000 people have been killed in the Syrian civil war.
Ban and US Secretary of State John Kerry told reporters before talks at the UN headquarters that there could be no military solution to the 28-month-old conflict.
While Syrian activists say well over 100,000 people have been killed, the UN has been more cautious about the toll.
But Ban said: "More than 100,000 people have been killed, millions of people have either been displaced or become refugees in neighbouring countries.
"We have to bring this to an end, the military and violent actions must be stopped by both parties and it is thus imperative to have a peace conference in Geneva as soon as possible."
The US and Russia have vowed to press for a follow up to a peace conference held in Geneva last year, which set out a transition plan.
Divisions between Syrian opposition groups and diplomatic hurdles thrown up by President Bashar al-Assad's government have blocked efforts to call a new meeting.
Syrian National Coalition president Ahmad Jarba is in New York and was to hold talks with Kerry ahead of a meeting with UN Security Council envoys on Friday.
Ban has previously said he would like a peace conference in September. But UN diplomats say the conflict is now so bitter that they doubt the two sides can be brought to the negotiating table.
Kerry said there is "enormous levels of suffering, suffering that is growing by the day which requires all of us to work even harder to try to bring about peace negotiations".
He added: "There is no military solution to Syria, there is only a political solution. That will require leadership in order to bring people to the table."
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