Pakistan has delivered a revised peace proposal from Iran to the US, sources in Islamabad told reporters on Monday.
According to Reuters news agency, both sides were warned that they "don't have much time" to narrow their differences before the situation escalates again.
Without providing details of the changes, the source told Reuters that Washington and Tehran "keep changing their goal posts."
Although a fragile six-week ceasefire remains in place, talks led by Pakistan have continued to stall and US President Donald Trump has said that the current truce is "on life support."
One of the major sticking points is Washington's call for Tehran to stop its nuclear program and its de facto blockade of the Strait of Hormuz, a key waterway that controls the flow of one-fifth of the world's oil and liquified natural gas. For its part, Iran wants compensation for war damage as well as an end to all hostilities, which includes Israeli strikes in Lebanon.
