The North fired the missiles from a mountain site just north of the border with South Korea and days after the beginning of annual joint US and South Korean military exercises, which the North routinely denounces as preparation for war.
The North and its leader Kim Jong-un were angered earlier this month when a nuclear-capable US B-52 bomber made a sortie over South Korea, though the flight did not trigger a sharp escalation of military tension.
The weapons fired yesterday were believed to be Scud short-range missiles, with a range of about 125 miles which means they can hit targets in South Korea but can not reach Japan.
Ties between the two Koreas are often fraught but this month hundreds of South Koreans crossed into the North to be reunited with family members not seen since the 1950-53 Korean War.
The reunions, a rare show of cooperation between the two Koreas, were held despite North Korean anger over the joint military exercises between South Korea and the US. Last year, the exercises triggered weeks of North Korean threats of war.
Earlier this week, South Korea offered North Korea help with an outbreak of foot-and-mouth disease in pigs, which would be the first government-level humanitarian help since 2010.