WASHINGTON, April 7 (Reuters) - A personal envoy of U.N. Secretary-General Antonio Guterres plans to visit Iran as part of his efforts to encourage an end to the Iran war, but his travel plans will depend on security and logistics, a U.N. source said.

Jean Arnault, a veteran U.N. diplomat Guterres named as his envoy on the conflict last month, headed to the Middle East on Monday, but the U.N. has not announced details of his itinerary.

Iran's U.N. ambassador, Amir Saeid Iravani, told the U.N. Security Council on Tuesday the envoy was "currently en route to Tehran to pursue consultations."

However, the U.N. source, who spoke on condition of anonymity, said Arnault's travel plans would be "contingent on security and logistics."

U.S. President Donald Trump threatened a dramatic escalation of the U.S.-Israeli war on Iran on Tuesday, saying that "a whole civilization will die tonight" as his deadline for Tehran to open the Strait of Hormuz neared.

With just hours to go before Trump's 8 p.m. EDT (0000 GMT) deadline, a senior Iranian official told Reuters that Tehran was positively reviewing a request by Pakistan for a two-week ceasefire to give more time for diplomacy.

Iravani said Iran welcomed Guterres' efforts, including the appointment of Arnault, to secure an immediate end to the war.

"Iran stands ready to engage constructively with all genuine diplomatic efforts, including through Pakistan, Turkey, and Egypt, as well as diplomatic efforts by China and Russia, and supports any credible initiative capable of bringing about a sustainable end to this unlawful and unwarranted war," he said.

(Reporting by David Brunnstrom; Editing by Mark Porter and Cynthia Osterman)