During a visit to Abu Dhabi, he will say the prospect of Iran having nuclear weapons poses "the most immediate threat" to Middle East stability, and appeal to Tehran's neighbours to put pressure on President Mahmoud Ahmadinejad.
"A nuclear-armed Iran would be a decisive blow against those seeking to promote pragmatic and peaceful solutions to the region's problems," Miliband will say, according to a pre-released copy of his speech.
"The consequent nuclear arms race would be very dangerous. The acquisition of a nuclear weapon would strengthen Tehran's regional position, injecting its attempts to stoke up division and promote instability with much greater confidence."
Iran says its nuclear programme is intended only for civilian energy purposes only, but it has refused to comply with UN Security Council demands that it cease uranium enrichment activities.
European Union and United Nations sanctions on Iran are not intended to bring about regime change in Tehran, nor are they a prelude to military action, Miliband is to say, according to the advance text.
There is "much that the Arab countries could do to counter Tehran's claims that their quest for greater influence and their nuclear programme enjoys tacit support throughout the region," he is to say.
His speech suggests offering economic incentives to Iran to cooperate, as well as "clamping down on smuggling or tightening up export controls on goods which could support the development of nuclear weapons".
Miliband will also say Arab nations must become more engaged in resolving the Israeli-Palestinian conflict, saying: "For too long, the countries of the region have been kept at one if not several removes from the peace process".
A lack of progress is threatening this process, and if nothing changes, "I believe the prospect of peace could disappear forever."
"Why? Because the situation on the ground, that leaves too many people insecure, in poverty and despair, is rapidly undermining the political process," Miliband is to say, according to the advance text.
"And because while both sides are tiring of the conflict, they are also tiring, faster, of efforts to resolve it."
