United Nations Secretary General Ban Ki-moon says while the time is not yet right for new peace talks in Syria, failing to get a serious agreement soon will make a further escalation all too likely.

Ban said Thursday that his special envoy for Syria, Staffan de Mistura, has declined to set a date for a third round of talks because "the time is not yet mature."

"We don't want to have talks for the sake of talks. At the same time, I want to underline the great urgency of the deadline of early August set by the co-chairs of the International Syria Support Group," Ban said.

He also called on the Syrian government to allow unhindered humanitarian access within the war torn country, saying withholding access is a war crime.