(CNN) -- Two medium-range missiles have been loaded onto mobile launchers in North Korea and are ready to be launched, South Korea's semi-official Yonhap news agency reported Friday, citing military sources in Seoul.
A U.S. official with direct knowledge of the information told CNN on Thursday that missile and launch components had been moved to the east coast of North Korea in the "last few days."
The latest Yonhap report said the two missiles have now been hidden in an unidentified facility near the east coast.
In response, South Korea has sent Aegis destroyers equipped with advanced radar systems to both of its coasts, Yonhap said, citing navy sources.
The apparent deployment comes amid further threatening statements by North Korea and heightened tensions in the region -- a situation that "does not need to get hotter," a U.S. State Department spokeswoman said Thursday.
The move of the missile and launch equipment could mean that Pyongyang, which unleashed another round of scathing rhetoric Thursday accusing the United States of pushing the region to the "brink of war," may be planning a missile launch soon.
The components, the official said, are consistent with those of a Musudan missile, which has a 2,500-mile range, meaning it could threaten South Korea, Japan and Southeast Asia.
The United States has been looking for a hidden North Korean east coast launch site or mobile launchers, a concern because a missile launched from the east coast would go over Japan, the official said.
South Korean officials also believe the weapons on the launchers are Musudan missiles, according to Yonhap.
It is believed a missile launch would be a "test" launch rather than a targeted strike. That is because it appears the North Koreans have only moved the components so far. The United States is waiting to see whether North Korea issues a notice to its airmen and mariners to stay out of the region.
Communication intercepts in recent days also seem to show that Pyongyang might be planning to launch a mobile ballistic missile in the coming days or weeks, another U.S. official said.
Earlier, South Korean Defense Minister Kim Kwan-jin told a parliamentary committee in Seoul that the North has moved a medium-range missile to its east coast for an imminent test firing or military drill.
The missile doesn't appear to be aimed at the U.S. mainland, Kim said, according to Yonhap.
Meanwhile, the British Foreign Office said North Korea told British officials that it would not be able to guarantee the safety of diplomats in Pyongyang in the event of conflict.
North Korea has asked the Russian Embassy in Pyongyang to consider a possible evacuation of its staff because of the tensions on the Korean peninsula, the press officer of the Russian Embassy in Pyongyang, Denis Samsonov, told Russian state media.
"The Russian side has taken note of this suggestion. No decision has been made yet," Samsonov said.
Wednesday, the United States announced it was sending ballistic missile defenses to Guam, a Western Pacific territory that is home to U.S. naval and air bases. North Korea has cited those bases when listing possible targets for missile attacks.
The latest developments come amid the disclosure of what one U.S. official calls an Obama administration "playbook" of pre-scripted actions and responses to the last several weeks of North Korean rhetoric and provocations.
Pentagon officials, while decrying North Korean saber-rattling, said recent announcements of U.S. military deployments in response to belligerent statements by North Korea may have contributed to the escalating tensions between the countries.
As the bombast reaches a fever pitch, the United States is refining its message toward North Korea. The Pentagon now says it is working to decrease the temperature as it maintains a frank and vigilant stance toward Pyongyang's threats.
The latest situation on the Korean Peninsula stems from the North's latest long-range rocket launch in December and underground nuclear test in February.
Tougher U.N. sanctions in response to those moves, combined with joint U.S.-South Korean military exercises in the region, are given by Kim Jong Un's government as reasons to ratchet up its threats in recent weeks.
Starting Wednesday, North Korea barred South Korean workers and managers from entering the Kaesong industrial complex, an economic cooperation zone that sits on the North's side of the border but houses operations of scores of South Korean companies.
It also repeated a threat from the weekend to completely shut down the complex, where more than 50,000 North Koreans currently work.
The current crisis at Kaesong began a day after North Korea said it planned to restart "without delay" a reactor at its main nuclear complex that it had shut down five years ago as part of a deal with the United States, China and four other nations.
Most observers say the North is still years away from having the technology to deliver a nuclear warhead on a missile.
It has conducted three nuclear bomb tests, in 2006, 2009 and most recently in February. It has said that its nuclear weapons are a deterrent and are no longer up for negotiation.
Many analysts say the increasingly belligerent talk is aimed at cementing the domestic authority of Kim Jong Un.
CNN's Jethro Mullen reported and wrote from Hong Kong. CNN's Barbar Starr reported from Washington. CNN's Laura Smith-Spark wrote in London. CNN's Kyung Lah, Judy Kwon and K.J. Kwon contributed in Seoul; Tim Schwarz in Hong Kong; Joe Sterling and Henry Shirley in Atlanta; Elise Labott and Tom Cohen in Washington.