In January, explosive-laden drones crashed into the main royal palace in Riyadh, with American media citing US officials as saying they were launched from neighbouring Iraq.

Saudi officials did not publicly disclose any details on the reported attack on the sprawling Al-Yamama complex, the official residence and office of King Salman as well as the main base of the royal court.

But the news raised alarm in a country that has frequently come under missile and drone attacks from Iran-aligned Huthi rebels in Yemen, where Riyadh-backed forces are engaged in a six-year conflict.

A relatively unknown militant group in Iraq calling itself the Righteous Promise Brigade claimed responsibility for the strike, but it was considered by security experts to be a front for more entrenched Iran-backed militias.

Kadhemi said the group's claim was "not true" and insisted that the attack was not launched from Iraq.

"We will not allow any attack on the kingdom," he told reporters after what his aides described as an hours-long meeting with Saudi Arabia's de facto ruler Crown Prince Mohammed bin Salman.

"There haven't been any attacks" from Iraq.

"There have been attempts by some to... disrupt relations" between Iraq and Saudi Arabia, he added, without elaborating.

Known to maintain close personal ties with Prince Mohammed, Kadhemi walks a diplomatic tightrope as Baghdad often finds itself caught in the tug of war between Tehran and its rivals Riyadh and Washington.

Kadhemi's trip comes after the countries reopened their Arar land border crossing in November for the first time since Riyadh cut off diplomatic ties with Baghdad in 1990, following Iraqi ex-dictator Saddam Hussein's invasion of Kuwait.

- Boosting trade, investment -

Aside from a discussion on border security, the Iraqi premier said he and his delegation of senior ministers sought to further boost trade and economic cooperation with the kingdom during a day-long visit to Riyadh.

In a statement published by Saudi state media, the two countries agreed to establish a joint fund with an estimated capital of $3 billion, a "contribution from the kingdom" to boost investment in the Iraqi economy.

Saudi Arabia's investments in Iraq are expected to rise to 10 billion riyals ($2.67 billion) from just over 2 billion riyals currently, the state-run SPA news agency said.

The countries also agreed to maintain energy cooperation to maintain stability in global oil markets, the joint statement added.

Iraq is the second-largest producer in the OPEC oil cartel, outranked only by Saudi Arabia.

Kadhemi, whose government has sought to fast-track foreign investment including Saudi support for energy and agriculture, is pushing for deeper cooperation with Riyadh.

Kadhemi was scheduled to travel to Saudi Arabia on his first foreign trip as prime minister last July, but the visit was cancelled at the last minute when King Salman was hospitalised for surgery to remove his gall bladder.

His trip to Tehran, Riyadh's arch-rival, went ahead, with the premier meeting Iran's supreme leader Ayatollah Ali Khamenei.