A report from the institute said: "As of June 2016, North Korea has about 13-21 nuclear weapons, where one weapon was subtracted to reflect the underground test in early 2016".
Mr Amano was referring to the Dispatch of a U.S Navy Strike group to the Western Pacific as a response to a series of banned missile tests.
"Military force can not resolve the issue", Chinese Foreign Minister Wang Yi told reporters in Beijing.
Trump has diverted the USS Carl Vinson aircraft carrier group towards the Korean peninsula, which could take more than a week to arrive, in a show of force aimed at deterring North Korea from conducting another nuclear test or launching more missiles to coincide with important events and anniversaries. Instead, the country is gearing up for its biggest holiday of the year, the 105th anniversary of the birth of the late Kim Il Sung, the country's founder and leader Kim Jong Un's grandfather.
Enter: China and North Korea.
That would be the sixth test over a two-year span.
The Communist Party-affiliated Global Times newspaper has indicated a willingness in the Chinese government to support stronger measures against North Korea.
The extent of North Korea's nuclear capabilities is shrouded in mystery because Kim Jong-un's regime is so secretive and isolated from the rest of the world.
Iraq says Islamic State has lost most of the land it seized
The operation began in October 2016 and led to the liberation of Mosul's eastern part this January. In Syria itself, it also holds the city of Raqqa and other areas.
Around 200 foreign journalists gathered in Pyongyang for North Korea's biggest national day, the "Day of the Sun", were taken to what was billed by officials as a "big and important event" early on Thursday.
It turned out to be the opening of a new street in the centre of the capital, attended by leader Kim. In 2012, it tried but failed to launch a long-range rocket carrying a satellite to mark the date and tested a newly developed intermediate-range missile past year.
"Commercial satellite imagery of North Korea's Punggye-ri Nuclear Test Site from April 12 shows continued activity around the North Portal, new activity in the Main Administrative Area, and a few personnel around the site's Command Center", the North Korea-related analysis website said. The North is technically at war with the United States and South Korea after the 1950-53 Korean War ended in a truce and not a peace treaty.
"If Trump were to follow through with his hints that he may give the order to shoot down any North Korean missile tests, it could lead to military escalation on both sides".
Satellite images suggest North Korea is preparing to conduct a nuclear test, its sixth since 2006, according to US -based monitoring group 38 North. Trump has put North Korea on notice that he will not tolerate provocative actions.
On Thursday, the North's state-run Korean Central News Agency (KCNA) said Kim watched from an observation post as special forces dropped from light transport planes "like hail" and "mercilessly blew up enemy targets". "It is beyond dispute for us to maintain normal trade relations with North Korea while observing our obligations to the Security Council resolutions", Lu said.