On April 29th, Pakistan ran another test of it's Hatf VI ballistic missile. This missile is a major advance over the Hatf V, which is actually the North Korean Nodong 1 missile, which was also sold to Iran, where it is called the Shihab 3. The Nodong 1 is basically a scaled up Russian SCUD missile, which, in turn was based on the first military ballistic missile, the German World War II V-2. Iran is believed to have paid $20 million for each of the North Korean Nodong 1s, while Pakistan is believed to have paid less (because of side deals relating to other weapons technology). The Hatf VI, on the other hand, uses solid fuel rockets. There are more difficult to manufacture, but are easier to use and more reliable. North Korea has mastered solid fuel rocket technology, and is apparently selling it to it's usual customers, Iran and Pakistan. While manufacturing requires exacting manufacturing procedures, solid fuel rocket motors are easier to handle, and have a shelf life of 10-15 years, if you make them right.
With the successful test of the Hatf VI, Pakistan now has all range classes covered by solid fuel missiles. The 1.5 ton Hatf I, which appeared in 1989, has a range of 80 kilometers and a half ton warhead. Also showing up in 1989, the 2.5 ton Hatf II has a range of 180 kilometers, and also carries a half ton warhead. The four ton Hatf III, which was first tested earlier this year, appears to be based on the Chinese DF-11. China has long been selling military technology to Pakistan. This missile has a range of some 300 kilometers and also carries a half ton warhead. The 6.3 ton Hatf IV also appears to be a Chinese design (the DF-9), has a range of 700 kilometers, uses solid fuel and has a .7 ton warhead. Pakistan began producing the Hatf IV in the late 1990s, although it was not tested until 1999.
The sixteen ton Hatf V is the only remaining liquid fuel missile. First tested in 1998, it has a range of some 2,000 kilometers and carries a .7 ton warhead. However, this missile will probably be quickly replaced by the recently tested Hatf VI. This missile was first publicly displayed in 2000, but has apparently undergone more years of development. The Hatf VI had a successful test last year, and has a maximum range (with the proper guidance system) of 2,500 kilometers.
The major problem with all Pakistani missiles is the electronics. Some of this is the control systems, but mostly it is the guidance system. You don't need a high degree of accuracy if you are using nuclear warheads. But it is believed that Pakistan has not yet mastered the intricacies of nuclear warheads for ballistic missiles. This is one of the more difficult engineering chores when building an ICBM system, and the last one new nuclear powers master.