The Press Trust of India said the suspect had claimed to work for an Iranian news organization, a fact Indian police declined to confirm.
Though Indian authorities have not implicated Iran in the bombing, any leads that point in that direction could complicate India's delicate efforts to ward off growing Western pressure and maintain its strong economic ties with Tehran.
Energy-starved India remains a large market for Iranian oil, and those purchases could blunt the effect of intensified sanctions being imposed by the United States and European Union to force Iran to roll back its nuclear ambitions.
"India finds itself between a rock and a hard place over Iran," said Arundhati Ghose, a retired Indian diplomat. "It's a tough call for the government, but one that New Delhi will have to confront eventually."
Police arrested Syed Mohammed Kazmi on Tuesday after investigations showed he had been in touch with a suspect they believe may have stuck a magnetic bomb on an Israeli diplomat's car, police spokesman Rajan Bhagat said.
Police said they searched Kazmi's house over the past two days to gather evidence that might link him to the Feb. 13 attack, which wounded the diplomat's wife, her driver and two other people in a nearby car. Police did not say what evidence they found.
Kazmi, 50, was being questioned and was scheduled to appear in court Wednesday before being handed over to officials of the investigating agencies for further questioning, Bhagat said.
The New Delhi blast came the same day a bomb was discovered on an Israeli diplomat's car in the former Soviet republic of Georgia. The next day, three Iranians accidentally blew up their house in Thailand, and Israeli authorities said the similarity between their explosives and the two earlier bombs linked Iran to all three incidents.
Indian officials have refused to assign blame while the investigation continues.
Israel has accused Iran of waging a covert campaign of state terrorism and has threatened military strikes on Iranian nuclear facilities.
If Kazmi's arrest and interrogation leads to evidence of Iran's involvement -- either directly or through its proxies -- in the New Delhi attack, the fallout could put India in a diplomatic quandary.
Iran is one of India's major suppliers of oil, accounting for 12 percent of its energy needs.
So far, India has fended off criticism for its growing economic ties with Iran by saying it does not heed unilateral sanctions, such as those being imposed by the United States and European Union.
"We have accepted sanctions that are made by the United Nations," Foreign Secretary Ranjan Mathai told reporters in Washington at a recent press briefing. "Other sanctions do not apply to us."
Western sanctions have made it harder for Indian companies to pay for Iranian oil, with international banks unwilling to handle transactions from Tehran without breaching the new American sanctions on Iran's financial earnings from oil.
Last month, India and Iran agreed to an arrangement for 45 percent of the $11 billion in annual oil payments to be made in Indian rupees, with the rest to be paid in a barter system.
Tehran is looking to trade oil for Indian-made machinery, iron and steel, minerals and automobiles, while Indian companies plan to invest in infrastructure projects in Iran including developing oil and gas fields, roads and railways.
India brushed off the international outrage over the blasts and said it would go ahead with a visit to Tehran this weekend by an Indian trade delegation headed by the commerce secretary.
"India needs the Iranian crude. It would be very difficult to find alternative sources of oil that would be acceptable to Indian refineries," a commerce ministry official said on condition of anonymity because he was not authorized to speak to the media.
Many of India's aging oil refineries are configured to use Iranian crude oil. Retrofitting these refineries would be costly, the official said.
India is also looking after its strategic interests in Iran's neighbor Afghanistan, which India hopes to prevent from falling under the sway of its archrival, Pakistan, after the 2014 withdrawal of NATO troops.
India uses Iranian ports to send goods to Afghanistan as it scrambles to maintain influence there.
"India is now in a panic over what lies ahead in Afghanistan. The Americans are leaving Afghanistan; they are talking to the Taliban. India will find itself scrambling for access in Afghanistan," says K.C. Singh, a former Indian ambassador to Iran.
To this end, India is helping develop the southern Iranian port of Chabahar and a rail link that will offer it direct access to Afghanistan.
New Delhi has not remained completely immune to sanction pressures and is slowly easing its dependence on Iranian oil.
Trends show a gradual decline in Iranian oil imports, with a temporary spike in January due to the bunching of earlier supplies that were delayed due to payment hurdles.
India has also developed close ties with Israel after diplomatic relations were established in 1992, and Tel Aviv has emerged as an important arms supplier.