A day after North Korea’s artillery attack on a South Korean island, a US aircraft carrier is on its way to Korean waters.
Observers say the move is likely to anger Pyongyang and unsettle its ally China, which is facing growing pressure to deal with its neighbour.
South Korea has vowed to strike back if it suffers another North Korean attack, and the US says it is standing firmly behind Seoul.
US President Barack Obama said: “South Korea is our ally. It has been since the Korean war, and we strongly affirm our commitment to defend South Korea as part of that alliance.”
North Korea is accusing Seoul of worsening ties on the peninsula with what it calls “reckless military provocation”.
The North says it opened fire because of military exercises carried out by the South; but Seoul denies that it fired towards the North.
Two South Korean soldiers were killed and the bodies of two civilians thought to have died in the attack have reportedly been found today.
Three other civilians were injured and dozens of others had to be evacuated from the island.
The artillery attack is being described as the heaviest in the region since the Korean war ended in 1953.
The international community has called for maximum restraint on both sides.