0216 GMT November 18, 2019
"Iran and Iraq are two nations whose hearts & souls are tied together through faith in God, love for Imam Hussein and the progeny of the Prophet (PBUH). This bond will grow stronger day by day," the Leader's official Twitter account cited Ayatollah Khamenei as saying.
"Enemies seek to sow discord but they've failed & their conspiracy won't be effective," he added.
State news agency IRNA said the Leader was reacting to recent violence in Iraq.
More than 100 people have been killed in Iraq since clashes erupted last week between protesters and security forces, the majority of them struck by bullets.
The Iraqi authorities have accused "saboteurs" and unidentified snipers of targeting the protesters.
Since the protests broke out last week, some officials in Iran have blamed the country's foes – including the United States, Saudi Arabia and Israel – for the Iraqi unrest.
"Foreign evil hands... are now seeking to destabilize Iraq in another way," said Hossein Amir-Abdollahian, a senior foreign policy advisor to Iran’s Parliament.
"This plot will also be foiled," he added in a tweet on Friday.
On Monday, government spokesman Ali Rabiei said there "are ill-wishers who seek to sabotage any opening between us and those neighbors who've had differences of opinions in recent years".
Call for 'self-restraint'
Speaking at a news conference aired on national television, Rabiei said Iran was "concerned and sad regarding any unrest in neighboring countries".
Iran called on "the great people of Iraq to show more self-restraint and seek democratic and legal means to reach their demands", he said.
"As always, the Islamic Republic of Iran expresses its readiness to stand beside Iraqi brothers and sisters and help them. No form of propaganda can sever the people of Iran and Iraq."
Iran has urged its citizens planning to take part in a major Shia pilgrimage in Iraq to delay their travel into the country over the violence.
Last week, Iran shut the Khosravi border crossing with Iraq at the request of Iraqi authorities as the protests raged.
The post was reopened on Monday morning and Iranians were making their way toward holy shrines in Iraq, an official said in a report by ISNA news agency.
A top military adviser to Ayatollah Khamenei said those behind the unrest would be unable to deter Iranian pilgrims.
"They want to scare people into not going to Arbaeen, but even if it rains arrows and stones, Hussein's lovers will not be afraid," Major General Yahya Rahim Safavi was quoted as saying by Tasnim news agency.
Iranians are heading to the Iraqi holy city of Karbala for the pilgrimage that will culminate on October 17 with the annual Arbaeen commemoration.
Arbaeen is one of the world's biggest religious ceremonies and marks the end of the 40-day mourning period for the seventh-century martyrdom of Imam Hussein (PBUH).
AFP and Press TV contributed to this story.