RIYADH - The Middle East's largest ever war games are now underway and will boost military cooperation between the 20 Muslim nations taking part, host country Saudi Arabia said on Monday, as it seeks to check the growing influence of arch rival Iran.

The Northern Thunder exercises, which began on Feb. 14 and will run until March 10, involve more than 150,000 troops from the Gulf Arab nations, Egypt, Morocco, Pakistan, Bangladesh, Jordan, Sudan and Senegal.

"The council of ministers ... expressed the hope that these exercises achieve what was defined as their goals in exchanging expertise and raising the level of military coordination," Saudi Arabia's cabinet said in a statement.

The statement also praised "the levels of preparedness and administrative and supply capabilities" shown by the nations participating in Northern Thunder exercises.

Riyadh, which is contributing the bulk of the troops in the war games, is also worried by the reduced regional role of its key ally, the United States and is seeking to build alternative military alliances as a counterweight to Iran.

Saudi Arabia is leading a coalition of Muslim countries, backed by the United States, Britain and France, in a war in neighbouring Yemen and says it will contribute troops if Washington leads land operations against Islamic State in Syria.Its war in Yemen, aimed at restoring a government ousted by an Iran-allied militia, is part of a more assertive effort by Riyadh since last year to counter Tehran's influence.

Meanwhile, Saudi Arabia has put 32 people on trial, including 30 members of its own Shia minority, accused of spying for Iran, several local newspapers and television reported on Monday.

The 32, including an Iranian and an Afghan, were detained in 2013 sparking expressions of concern among Saudi Shias who said that several were well known figures in their community and not involved in politics.

The trial is the first in recent memory for Saudis accused of spying and may stoke tensions between local communities and with Iran, which strongly denied the accusations at the time. The bitter rivalry between the kingdom and Iran has aggravated wars and political struggles in Syria, Iraq, Lebanon, Yemen and Bahrain and is regarded by many analysts as a cause of regional instability.

Tensions escalated further in January when Riyadh broke off diplomatic ties following the storming of its Tehran embassy by protesters angered at Saudi Arabia's execution of a Shia cleric convicted of involvement in the killing of policemen. Riyadh's Bureau of Public Prosecution presented the charges against the 32 on Sunday at the Specialised Criminal Court, which tries security offences, the Saudi-owned al-Arabiya channel reported.

The charges included establishing a spy ring with members of Iranian intelligence and passing them sensitive military information, seeking to sabotage Saudi economic interests, undermining community cohesion and inciting sectarian strife.

They also included supporting protests in the Shia-majority region of Qatif in Eastern Province, recruiting others for espionage, sending encrypted reports to Iranian intelligence via email and committing high treason against the king. The 32 were also charged with owning banned books and other publications, al-Arabiya and other Saudi-owned media reported.

Among those arrested in 2013 were an elderly university professor, a paediatrician, a banker and two clerics. Most were from al-Ahsa, a mixed Shia and Sunni region that is home to around half the members of the kingdom's minority sect.

Saudi Arabia has blamed sporadic unrest among Shias in Qatif on Iran, but has never publicly presented evidence of a direct link between those who took part in protests from 2011-2013 and Tehran, which denies any involvement.

In 2012, it said the hacking that August of the computer network of state energy producer Saudi Arabian Oil Co (Saudi Aramco) had originated from servers in other countries and some analysts pointed the finger at Iran, which also denied that.