NEW DELHI (Reuters) - United States President Barack Obama will fly a 30-member delegation, including top officials and Republican foreign policy veterans, to Riyadh on Tuesday to meet new Saudi Arabian King Salman as the crisis in neighboring Yemen continues to boil.

The unscheduled trip to pay respects following the death last week of King Abdullah underscores a strengthening US-Saudi alliance that extends beyond oil interests to regional security.

Joining Mr Obama will be Republican statesmen James Baker, secretary of state in the George H.W. Bush administration, and Mr Brent Scowcroft, national security adviser to presidents Gerald Ford and George H.W. Bush, the White House said.

Ms Condoleezza Rice, secretary of state for President George W. Bush, Mr Stephen Hadley, national security adviser in that administration, and Republican Senator John McCain, who is often critical of Mr Obama's foreign policy, also will join. Mr Obama's Secretary of State John Kerry and Central Intelligence Agency Director John Brennan will be part of the delegation, as will top Obama advisers Susan Rice and Lisa Monaco.

Cutting short a three-day trip to India, Mr Obama's visit comes as Washington struggles with worsening strife in the Middle East and counts Saudi Arabia among its few steady partners in a campaign against Islamic State militants who have seized swathes of Iraq and Syria.

Mr Obama is slated to arrive in Riyadh at 3.25pm local time, and will leave around four hours later.

The security headache worsened last week with the takeover of Yemen's government by Iran-backed rebels - a setback to US efforts to contain Al-Qaeda militants there and to limit the regional influence of Shi'ite Iran.

The Yemen government's collapse will be of deep concern to Saudi Arabia because of the long border they share and because of the advance of Iran, Sunni Saudi's main regional rival.

Saudi Arabia's role in rallying Arab support for action with Western countries against the Islamic State in Iraq and Syria (ISIS) has won praise in Washington, which with other Western nations values the kingdom as an important market for defence equipment.

Following Abdullah's death last Friday, Mr Obama will try to get relations off to a smooth start with King Salman, who takes power after a period of sometimes tense relations between Washington and Riyadh.

"Whatever the final communique says, the subjects most likely to be discussed ... are Syria, Iran, ISIS, and oil prices," wrote Mr Simon Henderson, an expert on US-Saudi relations at the Washington Institute for Near East Policy.

"The most interesting question for President Obama will be whether King Salman and his team of advisers have an order of priority that differs from King Abdullah's."

US criticism of Saudi Arabia over its human-rights record has been muted and is likely to remain so. The Saudi authorities have been criticised by international rights groups for jailing activists, and for the public flogging this month of a blogger.

But the White House may feel pressure to at least give a nod to human rights concerns, insisting as it often does that Mr Obama takes up such issues in private with allied leaders.

Despite an alliance between the two countries that has long been a cornerstone of US Middle East policy, Riyadh has made clear its impatience with the Obama administration's failure to do more to oust Syrian leader Bashar al-Assad and its anxiety over US-led efforts to negotiate a nuclear deal with Iran.

This added to a sense among Saudi rulers that Mr Obama was neglecting old Arab allies, most notably with the US abandonment of Egyptian President Hosni Mubarak when he was toppled by mass protests in early 2011.

US-Saudi relations improved after Mr Obama made a fence-mending visit to Riyadh last March.