North Korea yesterday fired short-range missiles into the sea off its eastern coast, prompting a warning from South Korea over "reckless provocation".
The missile tests, the second in a week, were timed to coincide with annual South Korea-United States military exercises which kicked off a week ago and run until mid-April.
Two missiles were fired yesterday, both flying 500km into the Sea of Japan, which Koreans call the East Sea, according to South Korea's defence ministry. Four Scud missiles were fired in similar fashion on Thursday.
Both tests were condemned by Seoul, which urged the North to cease all testing immediately and warned it would consider calling for sanctions.
"The North is taking a double-faced stance by making conciliatory gestures on one hand and pushing ahead with reckless provocation on the other," spokesman Kim Min-seok said.
The Scuds are at the longer edge of the short-range spectrum, with an estimated reach of between 300km and 800km, making them capable of striking any target in the South.
It is not unusual for North Korea to carry out such tests, which often go unreported by South Korea. But Kim said the recent Scud firings were of particular concern.
"We believe that the North is testing various ballistic missiles with various ranges as a show of force to threaten us," he said.
Washington initially played down Thursday's firings, but later suggested they violated UN sanctions imposed on the North's missile programme.
UN Security Council resolutions prohibit North Korea "from launching any ballistic missile, and this includes any Scud missile", Pentagon spokesman Colonel Steven Warren said on Friday.
Pyongyang routinely condemns the South-US joint exercises as rehearsals for invasion.
Last year they coincided with a sharp and unusually protracted surge in military tensions that saw North Korea issuing threats of pre-emptive nuclear strikes.
By contrast, this year's drills began as relations between Seoul and Pyongyang were enjoying somewhat of a thaw.
They overlapped with the end of the first reunion for more than three years of families divided by the Korean War, an event that raised hopes of greater cross-border co-operation.
Pyongyang initially had insisted that the joint exercises be postponed until after the reunions finished. Seoul refused and in a rare concession the North allowed the family gatherings on its territory to go ahead as scheduled.
Analysts believe the missile tests reflect Pyongyang's need to flex its muscles after the reunion compromise.
Last week also saw an incursion by a North Korean patrol boat across the disputed Yellow Sea border that has been the scene of brief but bloody naval clashes in the past. No shots were fired and the vessel retreated to its side of the boundary after repeated warnings from the South Korean navy.
North Korea has hundreds of short-range missiles and has developed and tested several intermediate-range weapons, with limited success.
Its claims to have a working intercontinental ballistic missile have been treated with scepticism by experts, but there is no doubt that it is pushing ahead with an ambitious missile development programme.