SEOUL (Reuters) – North Korea fired several short-range projectiles into the sea on Thursday, hours after the U.N. Security Council voted to impose tough new sanctions on the isolated state and the South Korean president vowed to end Pyongyang’s “tyranny.”

The firing escalated tensions on the Korean peninsula, which have been high since North Korea recent nuclear test and long-range rocket launch, and set the South’s military on a heightened alert.

South Korea’s Defence Ministry said it was trying to determine if the projectiles, launched at 10 a.m. from the North’s east coast, were short-range missiles or artillery fire.

The firing came after the U.N. Security Council passed a unanimous resolution on Wednesday dramatically expanding sanctions on North Korea following its fourth nuclear test on Jan. 6 and a long-range rocket launch on Feb. 7.

Russian U.N. Ambassador Vitaly Churkin said North Korea’s action showed it had not taken the proper lesson from the latest round of sanctions.

A spokesman for the U.S. State Department said Pyongyang should “refrain from provocative actions that aggravate tensions and instead focus on fulfilling its international obligations,” while a Chinese Foreign Ministry spokesman said China hoped all parties could refrain from actions that escalate tension.

Japan’s U.N. ambassador, Motohide Yoshikawa, said the firing was North Korea’s reaction to the latest sanctions and, “They may do something more.”

South Korean President Park Geun-hye welcomed the tougher Security Council sanctions and repeated a call for North Korea to change its behavior.

“We will cooperate with the world to make the North Korean regime abandon its reckless nuclear development and end tyranny that oppresses freedom and human rights of our brethren in the North,” Park said at a Christian prayer meeting.

Park has been tough in her response to the North’s recent actions, moving from her earlier self-described “trustpolitik.”

Last month, Seoul suspended the operation of a jointly run factory project with North Korea that had been the rivals’ last remaining venue for regular interaction.

On Thursday, South Korea adopted a long-delayed security law to set up an anti-espionage unit and another law aimed at improving human rights in North Korea.

In its latest barrage of insults against South Korea’s leader, North Korea’s official media carried a commentary on Wednesday likening Park to an “ugly female bat,” fated to “die in the dreary cave, its body hanging down.”

(Additional reporting by Jessica Macy Yu in BEIJING David Brunnstrom in WASHINGTON and Michelle Nichols and Louis Charbonneau at the UNITED NATIONS; Editing by Alex Richardson and Bill Trott)