Valerie Amos, U.N. under-secretary-general for humanitarian affairs and emergency relief coordinator, will stay in Damascus for two days.
"As requested by the Secretary-General, my aim is to urge all parties to allow unhindered access for humanitarian relief workers so that they can evacuate the wounded and deliver essential supplies," she said.
The state-run Syrian Arab News Agency said Amos will meet with Foreign Minister Walid al-Moallem and will visit "some areas in Syria."
But it's unclear whether Amos will see the areas most ravaged by what many call the government's sustained slaughter of dissidents across the country.
At least 39 people were killed across Syria on Tuesday, said the Local Coordination Committees of Syria, a network of opposition activists. The deaths included 23 in the embattled city of Homs, the LCC said.
Among those killed in Homs on Tuesday were 13 people from two families who died in what the LCC called "a new massacre" in the countryside near the city's hard-hit Baba Amr neighborhood.
Also in Homs, the Syrian military targeted a bridge on the Orontes River near the Lebanese border that was used as a crossing by wounded civilians, dissidents and refugees fleeing to Lebanon, said the Syrian Observatory for Human Rights, another opposition group.
As many as 2,000 Syrians have crossed from Homs province into Lebanon since Sunday, according to Dana Suleiman, spokesman for the U.N. High Commissioner for Refugees in Beirut.
Eight wounded Syrian men crossed into the Lebanese village of El Qaa from Syria on Tuesday, a Lebanese Red Cross official said. They were taken to hospitals in northern Lebanon by the Red Cross, but one of the Syrians died, said the official, who did not want to be named because he is not authorized to speak to the media.
One man, his face pale, lay on a stretcher with blood on his abdomen and his arm.
Refugees also fled the northern Syrian city of Idlib after a threat of government shelling, according to the Binnish Coordination Committee, a local opposition group. The Syrian regime had threatened to shell the city of Idlib if rebel Free Syrian Army members there did not hand over their weapons, the group said.
Also Tuesday, preliminary discussions began among the five permanent members of the U.N. Security Council plus Morocco "about whether there is any possibility of reaching agreement around a potential text that would demand an end to the violence in Syria and demand immediate humanitarian access," said Susan Rice, U.S. ambassador to the United Nations.
Li, China's former ambassador to Syria, made the remarks upon his arrival in Damascus, saying that his visit is part of China's "positive and constructive" efforts to find a peaceful solution to Syria's crisis.
He added that the aim of his visit is to discuss ways of peacefully settling the Syrian crisis with Syrian officials.
Another diplomat - U-N representative Valerie Amos - is also expected in Syria on Wednesday.
"These discussions are just beginning and will continue," she said. "If and when it seems there is a basis for a meaningful and viable text, we will propose one to the full Security Council."
Western diplomats said the goal is to bring Russia and China into the fold by creating a less harsh version of the last draft resolution, which the two countries vetoed, that would emphasize the humanitarian situation. They said they want the Russians and Chinese to join the call for a "permissive environment" for humanitarian access.
But the United States and its allies insist the resolution puts the onus on the regime to stop the violence and will not give up on that issue. This is a nonstarter for the Russians and Chinese, who want any resolution to reflect that armed opposition rebels also bear responsibility.
The Syrian regime consistently has blamed the violence on "armed terrorist groups" and portrayed its forces as trying to protect the public interest and security. The Syrian government says that more than 2,000 security personnel have been killed in the violence.
CNN cannot independently confirm reports across Syria because the government has severely restricted the access of international journalists. But the vast majority of reports out of Syria indicate al-Assad's forces are slaughtering civilians in opposition hotbeds in an attempt to wipe out dissidents seeking his ouster.
The United Nations has said at least 7,500 people have died in the crackdown, while opposition activists put the toll and more than 9,000.