By Jana Choukeir
DUBAI, Sept 20 (Reuters) - Iran warned on Sunday against any big new attack by the United States and its allies, saying it had information such a move was being prepared, adding to the anxiety in a region already on edge after drone and missile strikes on Saudi Arabia.
Iran's military central command said on state media that any new attack would trigger sustained retaliation against US bases and interests, and that Washington's regional allies would be considered parties to the conflict.
It did not elaborate on the information it said it had about a coming US attack.
The US State Department issued a security alert on Saturday saying there was potential for unforeseen escalation in the Middle East and Americans should exercise more vigilance and be aware of possible flight cancellations and airspace closures.
Nearly seven months into the US-Iran war, neither side has looked ready to make major concessions needed to end the fighting and with global energy markets already stretched, the conflict continues to spill over into other crises around the region.
On Saturday Yemen's Iran-backed Houthis, who made major advances along Yemen's Red Sea coast after the country's civil war reignited this month, said they had carried out strikes in the Saudi capital Riyadh and on a major oil facility in the kingdom's Red Sea port of Yanbu.
Reuters video showed a massive plume of black smoke billowing from the area of Riyadh's main international airport after booms were heard in the Saudi capital overnight.
Saudi Arabia did not comment on the incident or the Houthi claims, though a Saudi-led coalition fighting the Houthis said it had foiled other attacks on the kingdom. The US State Department alert cited Houthi hostilities against Saudi Arabia, including civilian airports.
Recent escalation by the Houthis has forced Riyadh into a painful dilemma: continue airstrikes on the group to stop it seizing more Yemeni territory or step back in the hopes of averting drone strikes on critical infrastructure.
STRIKES ON SAUDI ARABIA
The Houthi gains along the coast mean the group's forces now sit on the Bab el-Mandeb Strait, giving them easier control over shipping travelling between the Red Sea and Asia and the ability to blockade the crucial waterway.
With Iran already having blockaded most shipping in the Strait of Hormuz, the oil-rich Gulf's energy exports are now almost entirely cut off from global markets, adding to pressure on global oil prices.
A US blockade of Iranian ports is meanwhile stopping Iran from selling its own oil, contributing to major problems in the Islamic Republic's economy.
With the war inflicting painful damage on all sides, however, there is little sign of a return to the interim ceasefire agreement that was struck in June but that fell apart in July amid disputes over its terms.
Iran reiterated on Sunday that it would not reopen the Strait of Hormuz until the terms of that June agreement, as it interpreted them, were met.
Iranian Parliament Speaker Mohammad Baqer Qalibaf said Iran would have to keep on fighting as well as negotiating, to push back its enemies and to consolidate any gains with diplomacy.
(Reporting by Jana Choukeir in Dubai; Additional reporting by Timour Azhari in Riyadh; Writing by Angus McDowall; Editing by Aidan Lewis)
