After one week, Myanmar silent on whereabouts of detained Reuters journalists

* Reuters' Adler calls for journalists' immediate release

* Spokesman says they being treated well, in good health-report

* Myanmar's president authorises police to go ahead with case

* EU foreign affairs chief says arrests a "cause of real concern" (Adds U.S. State Department comment in paragraphs 13 and 14)

YANGON, Dec 19 (Reuters) - Two Reuters journalists completed a week in detention in Myanmar on Tuesday, with no word on where they were being held as authorities proceeded with an investigation into whether they violated the country's colonial-era Official Secrets Act.

Journalists Wa Lone, 31, and Kyaw Soe Oo, 27, were arrested last Tuesday evening after they were invited to dine with police officers on the outskirts of Myanmar's largest city, Yangon.

"We and their families continue to be denied access to them or to the most basic information about their well-being and whereabouts," Reuters President and Editor-In-Chief Stephen J. Adler said in a statement calling for their immediate release.

"Wa Lone and Kyaw Soe Oo are journalists who perform a crucial role in shedding light on news of global interest, and they are innocent of any wrongdoing."

The news group Democratic Voice of Burma (DVB) on Tuesday cited government spokesman Zaw Htay as saying that the journalists were "being treated well and in good health".

It gave no further details in its online report.

Reuters was unable to reach Zaw Htay for comment.

Myanmar's civilian president, Htin Kyaw, a close ally of government leader Aung San Suu Kyi, has authorised the police to proceed with a case against the reporters, Zaw Htay said on Sunday.

Approval from the president's office is needed before court proceedings can begin in cases brought under the Official Secrets Act, which has a maximum prison sentence of 14 years.

The two journalists had worked on Reuters coverage of a crisis that has seen an estimated 655,000 Rohingya Muslims flee from a fierce military crackdown on militants in the western state of Rakhine.

CRITICISM FROM FAR AND WIDE

A number of governments, including the United States, Canada and Britain, and United Nations Secretary-General Antonio Guterres, as well as a host of journalists' and human rights' groups, have criticised the arrests as an attack on press freedom and called on Myanmar to release the two men.

The U.S. State Department on Tuesday called for their immediate release.

"We've been ... following the cases of the two reporters, the Reuters reporters, very closely. We're deeply concerned about their detention. We do not know their whereabouts. That is of concern also," State Department spokeswoman Heather Nauert told a news briefing. "Today I want to make it clear that we're calling for their immediate release."