RIYADH/SANAA, Sept. 19 (Xinhua) -- Yemen's Houthi group said Saturday that it had launched large-scale attacks targeting the Saudi capital Riyadh and Yanbu, a major industrial and energy hub on Saudi Arabia's Red Sea coast, marking a major escalation in the confrontation between the two sides.

In a statement broadcast by Houthi-run al-Masirah TV, Houthi military spokesperson Yahya Sarea said the operations involved "a large number of ballistic and cruise missiles and drones."

Sarea said the first operation targeted what he described as "sensitive targets" in Riyadh, while the second struck a facility belonging to Saudi oil giant Aramco in Yanbu.

"The two operations were successful," Sarea said, claiming that large fires broke out at the targeted sites.

The Houthi statement came after explosions were heard in Riyadh twice on Saturday. Smoke was seen rising near King Khalid International Airport in the northeastern part of the capital following the second incident, while some flights were delayed.

Saudi authorities had earlier issued an aerial threat alert for Riyadh before announcing that the danger had passed, reportedly the first such alert for the Saudi capital since tensions between the Houthi group and Saudi Arabia intensified recently.

In a later statement, the Saudi-led coalition said that its air defenses intercepted and destroyed a Houthi ballistic missile targeting Riyadh and thwarted attacks on Baish, Taif, Farasan and Yanbu. Coalition spokesperson Turki Al-Maliki said the attacks targeted "civilians and civilian objects" and vowed "appropriate measures" to deter further attacks.

Sarea, the Houthi spokesperson, denied that the group deliberately targeted civilians, saying that the attacks against Riyadh were in response to intensified Saudi airstrikes on Houthi-held areas in Yemen.

The spokesperson vowed that the Houthis would continue retaliatory operations under what he called an "escalation for escalation" strategy until Saudi airstrikes cease and restrictions on Yemen are lifted.

The attack on Saudi's capital marks the latest escalation between Yemen's Houthi group and Saudi Arabia.

This round of conflict began in mid-July when the Yemeni Armed Forces struck Houthi-controlled Sanaa International Airport to prevent an Iranian passenger plane from landing. The plane carried a senior Houthi delegation returning from Iran after attending Khamenei's funeral ceremonies.

The Houthi group accused Saudi Arabia, a main ally of the internationally recognized Yemeni government, of launching the strikes and soon launched counterstrikes with ballistic missiles and drones in retaliation. It then announced a ban on Saudi shipping through the Bab al-Mandab Strait on July 20 and has since claimed a series of attacks on Saudi tankers and oil facilities in Saudi Arabia.

Yemen's conflict erupted in late 2014 when the Houthis seized the capital, Sanaa, and much of northern Yemen, prompting a Saudi-led coalition to intervene in March 2015 in support of the internationally recognized government.