As tensions mount following the US strike that killed a top Iranian general in Iraq, India's foreign minister on Sunday spoke to his counterpart in Tehran and expressed "concern" on developments that have "taken a very serious turn."

"Just concluded a conversation with FM @JZarif (Javad Zarif, Iran's Foreign Minister) of Iran. Noted that developments have taken a very serious turn. India remains deeply concerned about the levels of tension. We agreed to remain in touch," Minister of External Affairs S Jaishankar said in a tweet. 

The Ministry of External Affairs had on Friday said that the "increase in tension has alarmed the world."

"We have noted that a senior Iranian leader has been killed by the US. The increase in tension has alarmed the world. Peace, stability and security in this region is of utmost importance to India. It is vital that the situation does not escalate further. India has consistently advocated restraint and continues to do so," the MEA statement said.

On Friday, Iran's most senior commander Qassem Soleimani was killed by the US military at Baghdad airport in Iraq. Pentagon officials in the US later confirmed that the strike was carried out on the command of US President Donald Trump.

"At the direction of the President, the U.S. military has taken decisive defensive action to protect U.S. personnel abroad by killing Qasem Soleimani, the head of the Iranian Revolutionary Guard Corps-Quds Force, a US-designated Foreign Terrorist Organization," a statement by the United States Department of Defense read.

"General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region," it added.

The tensions continue to run high as US President Donald Trump has warned Iran that it has targeted 52 sites that 'will be hit very fast and very hard' if the country strikes any Americans or American Assets.

In a series of tweets, the US President said that Iran is talking very boldly about targeting certain USA assets in response to Soleimani's death. 

"Iran is talking very boldly about targeting certain USA assets as revenge for our ridding the world of their terrorist leader who had just killed an American, & badly wounded many others, not to mention all of the people he had killed over his lifetime, including recently... hundreds of Iranian protesters. He was already attacking our Embassy, and preparing for additional hits in other locations. Iran has been nothing but problems for many years. Let this serve as a WARNING that if Iran strikes any Americans, or American assets, we have..... targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran &  the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD. The USA wants no more threats!" he wrote on Twitter.

In another set of tweets a few hours later, Trump said, "They attacked us, & we hit back. If they attack again, which I would strongly advise them not to do, we will hit them harder than they have ever been hit before!"

"The United States just spent Two Trillion Dollars on Military Equipment. We are the biggest and by far the BEST in the World! If Iran attacks an American Base, or any American, we will be sending some of that brand new beautiful equipment their way...and without hesitation!" he added. 

Soleimani was one of the most powerful figures in Iran and as the head of the Quds Force, he directly reported to the Supreme Leader Ayatollah Ali Khamenei. 

Khamenei has vowed revenge against the killing of his general, saying "severe revenge awaits the criminals" behind the attack.