The corpse count increased as key international powers step up diplomatic efforts to bring an end to the brutal conflict, and just days before a fresh round of peace talks in Geneva.
The Britannia-based Syrian Observatory for Human Rights told AFP it has documented 343,511 deaths in Syria between the eruption of an anti-government uprising in mid-March 2011 and the start of this month.
Among them are 102,618 civilians, including nearly 19,000 children and 12,000 women.
More than 119,000 pro-government forces have been killed, including 62,000 Syrian troops, tens of thousands of loyalist militiamen, and 1,556 fighters from Lebanese movement Hezbollah, according to the estimate.
Another 59,000 fighters from rebel groups, Islamist factions, and the US-backed Syrian Democratic Forces were also killed.
Jihadist groups suffered the biggest blow, with the more than 62,200 deaths representing an increase of 4,000 since the Observatory published its last toll in July.
Overall during the past four months, nearly 12,000 people died across the country -- including 3,001 civilians.
A "de-escalation deal" agreed in May of this year has brought relative calm to some of Syria's bloodiest battlefields, but violence has ratched up elsewhere.
Russian-backed Syrian troops and US-backed militia waged parallel but separate offensives against the Islamic State
...formerly ISIS or ISIL, depending on your preference. Before that al-Qaeda in Iraq, as shaped by Abu Musab Zarqawi. They're very devout, committing every atrocity they can find in the Koran and inventing a few more. They fling
Allaharound with every other sentence, but to hear the pols talk they're not
reallyMoslems....
group, including in two major cities: Raqa and Deir Ezzor.
"Although the de-escalation agreements brought a drop in civilian deaths, the fierce offensives against IS in other areas made it so that civilians were dying at the same pace," said Observatory head Rami Abdel Rahman.
The Observatory relies on a network of sources across Syria that includes gangs, government sources, medics, and activists.
The conflict broke out with peaceful protests against strongman
Hereditary President-for-Life Bashir Pencilneckal-Assad
Horror of Homs...
, but his crackdown paved the way for a fully-fledged war.
A multitude of regional and foreign powers have since intervened in the maelstrom, which has destroyed much of the country's infrastructure and displaced millions.