The Syrian government has agreed to let aid workers into the country, the UN says, even as the government of Bashar al-Assad expels foreign diplomats.
It would be the first time humanitarian workers - aside from the International Committee of the Red Cross - have been granted permission to enter Syria.
The workers will initially be based in just four cities hard hit by the fighting: Homs, Deraa, Idlib, and Deir Azzor.
UN teams already have been sent to scout those areas, said John Ging, director of the co-ordination and response unit at the UN Office for the Co-ordination of Humanitarian Affairs.
"Whether this is a breakthrough or not will be evident in the coming days and weeks, and it will be measured not in rhetorics, not in agreements, but in action on the ground," he said.
But despite the humanitarian opening, Syria has also decided to declare 17 foreign diplomats unwelcome in the country.
The ambassadors of the US, UK, France and Turkey, among others, were declared personae non gratae.
Canada, Italy, Spain and various embassy staff members from Belgium, Bulgaria and Germany were also named in the foreign ministry's statement.
A group of mainly Western countries expelled Syrian diplomats in the wake of the Houla massacre of more than 100 people in late May, one of the worst atrocities in the country since an uprising broke out in March 2011.
Widespread violence continued on Tuesday, particularly in Latakia, a western port city, where 15 members of the security forces, three rebels and two civilians were killed, according to the London-based activists' network Syrian Observatory for Human Rights.
State media, for its part, reported the deaths of two high-ranking army officers at the hands of "terrorist groups".
Brigadier-General Anwar al-Saqqa was killed by a bomb planted under his car on the outskirts of Damascus, which also injured his daughter and driver, while Colonel Ahmad Abdul-Qader Haj Hattab was shot and killed by motorcycle-riding assailants in Deir Azzor, according to the SANA news agency.
Ceasefire constantly violated
Syria remains committed to the peace plan brokered by UN-Arab League envoy Kofi Annan, Faisal al-Maqdad, Syria's deputy foreign minister, said on Monday, following a meeting with the chief UN observer.
"We shall work for the success of Annan plan," Maqdad said, adding that he discussed with Major-General Robert Mood "the joint work that we need to carry out together after the full deployment" of the UN-backed truce observer mission in Syria.
Almost 300 UN unarmed military observers have been deployed in Syria to monitor a putative ceasefire in place since April 12, but which has been violated every day since then.
In-depth coverage of escalating violence across Syria
A Chinese official has said that Beijing and Moscow have been playing a "positive role" on Syria and reiterated the countries' opposition to foreign intervention in the conflict, as Russian President Vladimir Putin arrived for a three-day visit.
Putin's visit to China is aimed at bolstering crucial ties between the powerful neighbours who have aligned at the UN to block tougher international action against Syria despite widespread condemnation of the government's deadly crackdown.
Liu Weimin, a Chinese foreign ministry spokesman, told a daily news briefing that both countries agreed there should be an immediate end to violence and that political dialogue should begin as soon as possible.
"Both sides oppose external intervention in Syria and oppose regime change by force," Liu said.
"We believe ultimately the Syrian issue should be properly addressed through consultation among different parties in Syria. This is in the fundamental interests of the Syrian people. China and Russia have been playing, in their own way, a positive role on the Syrian issue."
Both energy and foreign policy co-operation are expected to be high on the agenda for Putin's visit, with the Russian leader also due to meet the presidents of Iran and Afghanistan as part of a regional security summit on Wednesday and Thursday.