Then, on Monday, the negotiations appeared doomed after the Syrian army declared an end to the US-Russian brokered ceasefire and a UN aid convoy was hit in an air strike.
But Kerry nevertheless took the opportunity of the ISSG members being gathered in New York for the United Nations General Assembly to convene crisis talks.
The mood was grim and the brief meeting inconclusive, but it allowed Kerry and UN peace envoy Staffan de Mistura a chance to insist that the process has not collapsed.
The talks lasted less than an hour and participants said the mood was tense but serious.
Kerry's spokesman John Kirby said the ministers had agreed that, "despite continued violence," they would still use the agreement between the United States and Russia as a basis for more talks.
The ISSG is thus to reconvene in New York this week.
"Quite frankly, the Kerry-Lavrov process is the only show in town and we've got to get that show back on the road," Britain's Foreign Secretary Boris Johnson admitted.
France was more openly skeptical, President Francois Hollande telling opposition figures that the truce hadn't lasted as long as the time it had taken to declare it.
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His foreign minister, Jean-Marc Ayrault, warned that trust was breaking down in the US-Russian partnership and said other countries should help push the process forward.
"It was a fairly dramatic meeting, the mood was gloomy. Is there hope? I can't answer that yet, but we should do everything we can," Ayrault told reporters.
"The Russians and the Americans can't do it alone."
Officials said participants had agreed to reconvene -- probably on Friday -- but analysts warned that more failures would not come without political costs.
Without a ceasefire, attempts to deliver aid to starving civilians or to broker a political dialogue will fail.
"A failed ceasefire means that the other two prongs of the approach are doomed," Emile Hokayem from the International Institute for Strategic Studies told AFP.
US officials have demanded that Russia take responsibility for what they said was an air strike on a UN aid convoy near the northern city of Aleppo by either Russian or Syrian warplanes.
The Russian defense ministry has denied any role in the attack, attempting to point the finger at rebels against Assad's regime.
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A short distance across Manhattan at the UN meeting, Secretary General Ban Ki-moon denounced the "sickening, savage and apparently deliberate attack" that left around 20 dead.
And Germany's Foreign Minister Frank-Walter Steinmeier confirmed that the convoy bombing had poisoned the mood at the ISSG, where delegates were "heavy with indignation."
Meanwhile, air raids and shelling continued on frontlines around Syria, where more than 300,000 have died since Assad began efforts to suppress a popular revolt.
The Syrian Observatory for Human Rights said at least 27 barrel bombs -- crude explosives packed with scraps of metal -- were dropped on Aleppo on Tuesday.
The International Federation of Red Cross and Red Crescent Societies said Monday night's raid destroyed at least 18 of 31 vehicles and a Red Crescent warehouse.
The strike came just hours after the Syrian army announced the end of the truce Monday, accusing rebels of failing to "commit to a single element" of the US-Russia deal.