Hot on the heels of unveiling its first indigenous short-range, air-defense missile system, Tehran asserts that it will manufacture advanced Russian S-300 missiles itself if Moscow persists in not delivering weapons Iran ordered in December 2005.

The Iranians also claimed they plan to develop their own radar systems to replace the aging Russian-built systems they currently deploy.

The flurry of Iranian announcements Sunday and Monday concerning the country's air-defense and technological capabilities were clearly linked to tension between the United States and Iran over its nuclear program.

That tension was heightened April 6 when U.S. President Barack Obama's unveiled a U.S. nuclear strategy that restricts the use of nuclear weapons but made clear that Iran and North Korea remain firmly in U.S. cross hairs.

Earlier, a U.S. think tank suggested that Israel, which has threatened to launch pre-emptive strikes against Iran's key nuclear facilities if U.S.-led diplomacy fails to convince Tehran to abandon its alleged quest for nuclear arms, could resort to using tactical nuclear warheads atop Jericho ballistic missiles.

All this seems to have rattled the Tehran regime and the announcements would appear to reflect that unease.

Iran's hard-line Defense Minister Gen. Ahmed Vahidi said the new air defense system, known as Mersad -- Farsi for "ambush" -- was going into mass production and that a "sizable number" would be operational by the end of the year.

Mersad, which on the face of it marks a milestone in Iran's aerospace technology, is based on the U.S.-build Hawk air-defense system sold to Iran in the 1970s when Shah Mohammad Reza Pahlavi was in power.

Vahidi said the indigenous Shahin missile, Mersad's main component, is more advanced than the Hawk. He gave no performance details but the Hawk had a range of 15 miles carrying a 119-pound warhead.

He claimed the new system is also equipped with advanced launch and radar technology with improved guidance and target acquisition systems.

But it is unlikely that the Mersad system has a heavily extended range or greatly enhanced killing power than the original.

And while Mersad may thicken Iran's surface-to-air missile defenses, these remain relatively short-range systems that leaves the country's nuclear facilities and other strategic targets, vulnerable to attack by aircraft or missiles.

Iran still has no long-range, high-altitude interceptor capable of repulsing airstrikes from a distance. That's why Tehran is so incensed by Moscow's refusal, clearly at the behest of the United States and Israel, to deliver the five batteries of S-300PMUs it signed for in the $700 million 2005 contract.

The truck-mounted S-300, considered to be on a par with the U.S. MIM-104 Patriot, can track dozens of targets, aircraft and missiles, simultaneously and shoot them down from a range of around 100 miles at altitudes of up to 40,000 feet.

Russia cites "technical difficulties" for the delay in delivery, which should have begun in 2008.

Iran's boast that it could manufacture S-300s on its own is in all likelihood a gross exaggeration that only serves to underline the depth of concern in Tehran about the serious gaps in its air-defense system.

That will be the country's primary defense against U.S. or Israeli strikes. The air force, badly hurt by U.S.-led international arms embargoes over the last 30 years, is in poor shape and would pose little threat to U.S. or Israeli jets.

Meantime, tension between Hezbollah, Iran's ally in Lebanon, and Israel has been mounting steadily for weeks with inflammatory rhetoric from both sides.

Israel and Hezbollah fought a 34-day war in 2006 in which Israel came off worst. Israeli military chiefs have warned that a new conflict is likely.

In that regard, Israeli President Shimon Peres accused Syria Tuesday of supplying Scud-type ballistic missiles to Hezbollah, adding to the armory of some 45,000 missiles of various calibers that Defense Minister Ehud Barak claims Hezbollah possesses.

Saddam Hussein used the Soviet-designed Scuds to bombard Iranian cities during the 1980-88 war. In the 1991 conflict, Saddam unleashed 88 Scuds, all with conventional warheads, against Israel and Saudi Arabia.

If the reports of deliveries to Hezbollah are true, the Syrian move would be dangerously provocative as Israel would deem the deployment of Scuds, even in limited numbers, on its northern border to be a serious threat to its security.