Saudi Arabia said Monday it was dealing with more drones and missile strikes as a slew of countries warned against travel to the Kingdom due to fatal attacks on Riyadh airport by Iran-backed Houthi militants.

The Australian and New Zealand governments on Monday cautioned their citizens against traveling to King Khalid International Airport in Riyadh and other Saudi destinations, joining similar advisories from the U.K., U.S., Canada, France, Germany, Japan and others.

It came as the Saudi aviation authority extended the suspension of operations at the airport, which has been hit by numerous projectiles over the last week. The deadliest strike came on Saturday, when 12 people were killed and more than 300 were injured, according to officials. Another strike on Sunday killed one person and injured nearly a dozen.

Yemen's Iran-backed Houthi rebels have claimed responsibility for the attacks, which have raised questions over the robustness of Saudi Arabia's defense capabilities despite its huge military spending.

The fatalities come as the Kingdom hosts major corporate conferences, including the World ⁠Petroleum Congress, the International Energy Forum Ministerial Meeting and the Future Investment Initiative.

U.S. President Donald Trump said on Sunday that the U.S. "may" join Saudi Arabia in its retaliation against the Houthis.

Iran's Foreign Minister Abbas Araghchi said on Sunday that he had told Saudi Arabian Minister of Foreign Affairs Prince Faisal bin Farhan Al Saud by phone that Tehran was willing to take steps to start dialogue between Saudi Arabia and Yemen, where the Houthis are based.

Iranian Foreign Ministry spokesperson Esmaeil Baghaei meanwhile said that Iran was still reviewing a U.S. response to its proposal for reopening of the Strait of Hormuz and would reply though its intermediaries, Reuters reported.