(CNN)-- US Secretary of State Marco Rubio said Monday that the United States will remain open to diplomatic dialogue with Iran, at a time when Washington launched airstrikes for the ninth consecutive night against Iran.

Rubio told reporters before leaving for Manila to attend the Association of Southeast Asian Nations (ASEAN) summit: 'The United States always remains open to a diplomatic solution. We have tried repeatedly with Iran, and we will continue to try. If that door opens, we will be happy to do so.'

Rubio also criticized Iran for attacking ships and obstructing navigation in the Strait of Hormuz, saying: 'A memorandum of understanding cannot remain in effect if they are violating its terms,' adding: 'They continue to send signals that they want dialogue and negotiation, but we respond to their behavior, which is launching missiles and drones at ships, including tonight.'

The memorandum of understanding signed between the United States and Iran in June aims to expand the ceasefire and facilitate navigation through this vital waterway.

In response to a question from CNN's Kate Maher about what would happen if diplomatic efforts failed, Rubio replied: 'I don't think that would be in Iran's interest. I mean, their economy is in a dire state.'

Rubio also addressed the incident that killed a US soldier in northern Iraq on Sunday, describing it as an 'accidental incident,' and that the US soldier was injured while dismantling an Iranian drone after it was downed.

The US minister told reporters: 'No job in the military is safe. It is inherently risky work, and we are grateful for these American heroes who wear the uniform and serve our country.'

Regarding the Iranian attack that killed two US soldiers in Jordan, Rubio said: 'A missile penetrated the defenses. We shot down almost all the missiles. One missile got through... It's heartbreaking.'

Rubio added that he 'prays for their families and prays for their souls.'

This brings the number of US soldiers killed in the ongoing war with Iran over the past five months to 17.