VIENNA (AP) ― As international tensions rise over a planned North Korean rocket launch, the U.N. nuclear agency is taking a wait-and-see attitude on an offer from the North to allow agency experts back into the country, according to a letter shared with the Associated Press.

In the March 30 letter, circulated internally among the International Atomic Energy Agency’s 35 member-nations, IAEA head Yukiya Amano expresses thanks for the March 16 overture by North Korean Atomic Energy head Ri Je-son and says “the IAEA will follow up on your invitation in a constructive spirit.”

At the same time, the letter appears to make some linkage between an IAEA mission to the North and whether a Feb. 29 agreement between Pyongyang and Washington can be salvaged despite North Korean plans for a long-range rocket launch in mid-April ― a launch the U.S. says would sabotage the deal.

North Korea says the missile launch is intended to place an observation satellite into orbit. But the U.S. and others among the five countries in sporadic talks with the North view the launch as a cover for a test of an intercontinental ballistic missile that one day could carry a nuclear warhead.

The rocket test was announced March 16, the same day Pyongyang invited the IAEA to visit.

Washington argues the launch would abrogate the Feb. 29 deal, under which the North would freeze nuclear activities and observe a moratorium on nuclear and long-range missile tests in exchange for 240,000 metric tons of food aid.

The letter says the IAEA has “an essential role to play in verifying’’ the North’s nuclear program. But it also notes that the tentative deal between Washington and Pyongyang that is now being threatened “is an important step in the right direction.”

The letter ― and another one with the invitation from the North ― was shared Tuesday with the AP by a diplomat from a board member nation who demanded anonymity because he was not authorized to share privileged material.

In recent days, IAEA officials have said privately that the agency and the North were discussing a timing and scope for any visit by agency experts as well as technical details.

But the careful diplomatic language in Amano’s response nearly two weeks after the North’s offer suggested the IAEA chief was awaiting events tied to the planned rocket launch before formally committing his agency to specifics.