The White House said Friday it "would not be surprised" if North Korean carries out another missile test, after reports that Pyongyang had moved two mid-range rockets to its eastern coast.
"We've obviously seen the reports that North Korea may be making preparations to launch a missile, and we're monitoring this situation closely," White House spokesman Jay Carney told reporters.
"We would not be surprised to see them take such an action. We have seen them launch missiles in the past ... And it would fit their current pattern of bellicose, unhelpful and unconstructive rhetoric and actions," he said.
"We urge them to stop with the provocations and to focus instead on meeting their international obligations and feeding their own people. They are only making themselves more and more isolated from the rest of the world."
The Pentagon declined to confirm reports about the missiles from South Korea's Yonhap news agency, but warned North Korea that "further provocative action would be regrettable."
"Missile tests outside their international obligations would be a provocative act. They need to follow international norms and abide by their commitments," Pentagon spokesman George Little told reporters.
Several UN Security Council resolutions require North Korea to abstain from all nuclear and ballistic missile activities.
Yonhap reported that two intermediate Musudan missiles had been transported by train earlier in the week and loaded on vehicles equipped with launch pads.
The Musudan has never been tested, but is believed to have a range of around 3,000 kilometers (1,860 miles), which could theoretically be pushed to 4,000 if they were to be given a light payload.
That would cover any target in South Korea and Japan, and possibly even reach US military bases located on the Pacific island of Guam.
The Pentagon has said it will send missile-interceptor batteries to protect its bases on Guam, a US territory some 3,380 kilometers (2,100 miles) southeast of North Korea and home to 6,000 American military personnel.
Most experts think the North is not yet capable of mounting a nuclear device on a ballistic missile which could strike US bases or territory.
Tensions have soared on the Korean peninsula since December, when the North test-launched a long-range rocket. In February, it conducted its third nuclear test and drew fresh UN sanctions.
The North also warned this week it would reopen its mothballed Yongbyon reactor -- its source of weapons-grade plutonium that was closed in 2007 under an aid-for-disarmament accord.
Little defended a current South Korean-US military drill, which has infuriated Pyongyang, saying "we have been responsible and prudent in how we (have) conducted these exercises," which run through April 30.
"The North Koreans on their side need to ratchet the rhetoric down, which has been bellicose, overheated and unproductive," he said.